Printing apparatus and control method therefor

ABSTRACT

In a printing apparatus having full-color and monochrome print processes and a method therefor, whether a page to be printed is color or monochrome is checked. The presence of an immediately preceding page which is successively printed before a page to be printed that is determined to be monochrome, and the attribute of the immediately preceding page are determined. The presence of a succeeding page which is successively printed after the page to be printed, and the attribute of the succeeding page are determined. The number of pages corresponding to the determination results is set. The print process of the page to be printed is decided on the basis of the presence of succeeding pages corresponding to the number of pages and their attributes.

FIELD OF THE INVENTION

The present invention relates to a printing apparatus capable ofprinting monochrome and full-color images and a control method thereforand, more particularly, to a color printing apparatus capable ofswitching between monochrome and color print modes on the basis ofsupplied print data, and a control method therefor.

The present invention also relates to a printing system which isconstituted by a full-color printer having monochrome and full-colorprint processes and its printer driver, and a control method therefor.

BACKGROUND OF THE INVENTION

As office automation progresses for deskwork, data transfer from a hostcomputer to a printing apparatus and printing documents, drawings, andthe like increases more and more. In recent years, it becomes popular tocreate documents and drawings in color. Printing apparatuses capable ofhigh-speed printing and printing apparatuses capable of color printingare being introduced more and more.

A color printing apparatus is not used to print only color documentsthough its principal object is to print color documents, and is oftenused to print monochrome documents. Such a color printing apparatus isutilized to print a document containing color and monochrome pages or toperform printing based on instructions from a plurality of users in anetwork. The trend of coexistence of color and monochrome documents isgrowing.

A conventional full-color page printer has both monochrome andfull-color print processes. The page printer generally prints amonochrome page by the monochrome print process and a full-color page bythe full-color print process for the purpose of high-speed output ofmonochrome pages, power saving, and reduction in the wear of afull-color printing mechanism by adopting a print process for monochromeprinting and printing a monochrome page in the monochrome print process.

In general, a color image forming apparatus such as a printingapparatus, color printer, or color copying machine has an engine forprinting (image transfer) by assembling (unitizing) developing units fora total of four toners: K (black) toner used to print characters and thelike, and Y (Yellow) toner, M (Magenta: red dye) toner, and C (Cyan:greenish blue) toner, which are three primary colors in subtractivecolor mixture.

In image transfer, the respective color units are operated tomulti-transfer the respective color toners onto a print sheet on thebasis of pixel information mapped in frame memories for the respectivecolors.

In this color printer, a document to be printed (image transfer) is notlimited to a color document. In practice, the color printer is used toprint both color and monochrome documents.

Generally, a monochrome document can be printed using only a K tonerprocess unit (to be referred to as a monochrome process unithereinafter: the remaining process units will be referred to as a colorprocess unit hereinafter).

In order to prevent degradation of the process unit by tonerconsumption, friction, and the like, some color printers have a functionof, when a print document is monochrome, separating the color processunit so as not to operate it, and operating only the monochrome processunit, thus preventing consumption of the color process unit.

Note that “operating the process unit” includes a state in which theprocess unit runs idle without any substantial printing, like the colorprocess unit during monochrome printing in a printer not equipped withthe above function.

If the above-mentioned printer can suppress the wear and powerconsumption of the full-color printing mechanism to reduce the printingcost of a monochrome page in a full-color printer close to the printingcost in a monochrome printer in printing a monochrome page, the userneither installs both monochrome and full-color printers nor selects thetype of printer in accordance with each document to be printed.

The prior art of using the monochrome and full-color print processes andswitching the print process, as needed is therefore indispensable forspreading full-color page printers.

An example of the color printer which switches the print process is atandem color printer which adopts one of typical processes of a colorimage forming apparatus. The tandem color printer comprises drums forrespective color components, and realizes high-speed print processing byarranging these drums parallel to each other on the convey path andperforming transfer of all colors by one process.

More specifically, the tandem color printer has a mechanism whichcomprises four photosensitive drums (photosensitive drums correspondingto four colors: cyan, magenta, yellow, and black) in order to increasethe color printing speed, and transfers an image onto a transfer mediumby four developing units.

Some tandem printing apparatuses have a mechanism which operates yellow,cyan, and magenta units not used for printing (e.g., idly operatesphotosensitive drums). Idle operation of photosensitive drumsexcessively shortens the service life of units such as yellow, cyan, andmagenta photosensitive drums.

In order to reduce toner consumption and the wear of each unit, a colorprinting apparatus of this type switches the operation between colorprint processing and monochrome print processing. In printing amonochrome document, the color printing apparatus controls to moveyellow, cyan, and magenta developing units except a black developingunit apart from the electrostatic convey belt so as not to print incolors except black.

That is, there has been proposed a color printing apparatus whichswitches between color print operation and monochrome print operation ofretracting the yellow, cyan, and magenta developing units in accordancewith supplied data contents so as not to shorten the service life of theyellow, cyan, and magenta units. If the supplied data is only monochromedata, printing is done by automatically switching the operation tomonochrome print operation.

As described above, the conventional full-color page printer realizeshigh-speed output, power saving, and protection of the full-colorprinting mechanism in printing a monochrome page by switching betweenthe monochrome and full-color page print processes. In general, printprocess switching operation requires a predetermined processing time,consuming power. In addition, print process switching operation loadsthe printing mechanism, and frequent switching of the print processshortens the service life of the printing mechanism.

For example, in printing a document in which color and monochrome pagesappear almost alternately, or in a use environment where a plurality ofusers frequently print a document of 1 or 2 pages, monochrome andfull-color pages are printed at random, and the print process will befrequently switched. In this case, even if the monochrome print processis higher in speed and lower in power consumption than the full-colorprint process, the processing time and power consumption in monochromeprinting increase owing to the processing time of print processswitching operation, power consumption, and print process switchingoperation. Printing all pages in the full-color print process may becomemore preferable in terms of the printing speed, power consumption, andload on the printing mechanism.

Shift from monochrome print operation to color print operation oropposite shift requires an operation such as retraction/return of thedeveloping unit due to the difference between monochrome and color printoperations. If print operation shifts, data cannot be kept printed,requiring a switching time.

For example, the above-described tandem color printer takes a switchingtime between color and monochrome print operations. To prevent this,there has been proposed a method of printing monochrome data in color toincrease the throughput without switching print operation under apredetermined condition when printing a document containing both colorand monochrome pages.

For example, Japanese Patent Laid-Open Nos. 11-34438 and 2000-29266disclose a method of printing a monochrome page as a target page in thefull-color print process under a given condition when an immediatelypreceding page is printed in the full-color print process.

In Japanese Patent Laid-Open No. 11-34438, print operation is switchedin terms of the throughput. That is, there is proposed a printingapparatus in which, when a monochrome image is received as an image tobe printed next during the color print mode, the printing time ofprinting the monochrome image in the color print mode and the printingtime of switching to the monochrome print mode and then printing theimage are compared, and if the printing time in the color print mode isshorter, the image is printed in the color print mode. According to thismethod, an engine which takes a very long time for switching from thecolor print mode to the monochrome print mode and always prints data ata high speed in the color print mode without switching it keeps printingmonochrome data in the color print mode once monochrome data is printedin the color print mode. This greatly shortens the service life of aunit such as a photosensitive drum in the tandem printing apparatus orthe like.

To the contrary, in the method proposed in Japanese Patent Laid-Open No.2000-29266, the print mode is switched in terms of toner waste and theservice life of each component. This method adopts an approach ofcalculating a disadvantage generated when monochrome data is printed inthe color print mode and a disadvantage generated when the mode isswitched to the monochrome print mode, and comparing these disadvantagesto decide whether to switch the mode. However, it is difficult toaccurately calculate the disadvantage, and when a print mode selected onthe basis of the disadvantage is determined to be switched, thethroughput may decrease.

These methods are based on switching to the monochrome print processwhen it is confirmed by referring to the attributes of pages subsequentto a target page that monochrome pages succeed to a given extent, i.e.,when switching to the monochrome print process is determined to beadvantageous. The attributes of a predetermined number of succeedingpages must be referred to.

Particularly when these methods are applied to a printing mechanism inwhich the print process switching time is relatively long with respectto the difference in the printing time of one page between themonochrome and full-color print processes, the next target page cannotbe printed until the page attributes of many pages are decided. Forexample, attention is paid to the printing time, and these methods areapplied to a printing mechanism in which the monochrome printing speedis 2 sec/page, the full-color printing speed is 3 sec/page, and the timetaken to switch the print process is about 10 sec. In this case, whenthe print process is switched from the full-color print process to themonochrome print process and returns to the full-color print processagain, printing upon switching to the monochrome print process does notprovide any merit from the viewpoint of the printing time unless thenumber of successive pages to be printed in the monochrome print processis at least 20 or more.

This means that a target page may not be printed unless 20 or moresucceeding pages are accumulated. To accumulate succeeding pages, theprinting mechanism may be kept idle.

These references define operation when a page immediately preceding atarget page is a full-color page. If no immediately preceding pageexists, i.e., print data starting from a monochrome page is to beprocessed while no print processing is done, the print process may notbe optimum depending on the condition.

Switching of the print process based on whether a document is color ormonochrome is achieved by separating each process unit from a sheet bymechanical operation. The print mode cannot be switched until the sheetis completely discharged.

One switching operation takes a very long time of about 10 to 30 sec.For this reason, every printing of color and monochrome pages by one jobrequires a switching time, which impairs high-speed operation which is amerit of the tandem printing apparatus.

This is not limited to a printing apparatus having the tandem printingengine. Also in the use of a single-head apparatus or intermediatetransfer member, the print mode is switched by separating each processunit from a sheet by mechanical operation. A long time is similarlytaken, and the printing speed decreases in the coexistence of monochromeand color pages.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the conventionalsituation, and has as its object to provide a printing apparatus whichmore efficiently decides the print process of a monochrome page toprevent a print processing delay and the wear of a device, and a controlmethod therefor.

It is another object of the present invention to provide a printingapparatus capable of optimizing decision of the print process bydetermining the print process of a monochrome page depending on notwhether a page to be printed is monochrome or full-color but thepresence/absence of immediately preceding and succeeding pages and theirattributes, and a control method therefor.

It is still another object of the present invention to allow the user toset a desired print mode in which data is printed in the full-colorprint process regardless of whether an object to be printed ismonochrome or full-color, and easily realize optimization of a printprocess corresponding to a print job.

It is still another object of the present invention to realize printmode switching processing which properly satisfies the service life of aunit and the print processing throughput.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a sectional view showing the arrangement of an LBP accordingto an embodiment of the present invention;

FIG. 2 is a block diagram for explaining the control arrangement of theLBP according to the embodiment of the present invention;

FIG. 3 is a view showing the structure of intermediate data according tothe embodiment of the present invention;

FIG. 4 is a flow chart showing the processing procedures of intermediatedata generation processing according to the embodiment of the presentinvention;

FIGS. 5A and 5B are flow charts showing the processing procedures ofprint process selection processing for a monochrome page according tothe first embodiment of the present invention;

FIGS. 6A and 6B are flow charts showing the processing procedures ofprint process selection processing for a monochrome page according tothe second embodiment of the present invention;

FIGS. 7A and 7B are flow charts showing the processing procedures ofintermediate data generation processing according to the third andfourth embodiments;

FIG. 8 is a view showing the print execution instruction window of aprinter driver according to the third embodiment;

FIG. 9 is a view showing the print execution instruction window of aprinter driver according to the fourth embodiment;

FIG. 10 is a block diagram showing the system configuration of a colorlaser beam printer according to the fifth embodiment;

FIG. 11 is a sectional view for explaining the engine unit of the colorlaser beam printer according to the fifth embodiment;

FIG. 12 is a flow chart showing processing steps in the imageinformation generator and color/monochrome mode setting unit of thecolor laser beam printer according to the fifth embodiment;

FIG. 13 is a flow chart showing processing steps in the printingexecution unit of the color laser beam printer according to the fifthembodiment;

FIG. 14 is a flow chart showing processing steps in the print modedecision unit of the color laser beam printer according to the fifthembodiment;

FIG. 15 is a view for explaining the operation of the print modedecision unit of the color laser beam printer according to the fifthembodiment;

FIG. 16 is a view for explaining the operation of the print modedecision unit of the color laser beam printer according to the fifthembodiment;

FIG. 17 is a flow chart showing processing steps in the print modedecision unit of a color laser beam printer according to the sixthembodiment;

FIG. 18 is a flow chart showing processing steps in the print modedecision unit of a color laser beam printer according to the seventhembodiment;

FIG. 19 is a view for explaining the operation of the print modedecision unit of the color laser beam printer according to the seventhembodiment;

FIG. 20 is a view for explaining the operation of the print modedecision unit of the color laser beam printer according to the seventhembodiment;

FIG. 21 is a flow chart for explaining the operation of the dischargecompletion monitoring unit of the color laser beam printer according tothe fifth embodiment;

FIG. 22 is a flow chart showing processing steps in the print modedecision unit of a color laser beam printer according to the eighthembodiment;

FIG. 23 is a view for explaining the operation of the print modedecision unit of the color laser beam printer according to the eighthembodiment;

FIG. 24 is a flow chart showing processing steps in the print modedecision unit of a color laser beam printer according to the ninthembodiment;

FIG. 25 is a flow chart showing processing steps in the print modedecision unit of a color laser beam printer according to the 10thembodiment;

FIG. 26 is a view for explaining pattern matching operation of the printmode decision unit of the color laser beam printer according to the 10thembodiment;

FIG. 27 is a block diagram showing the schematic configuration of animage printing system to which a printer according to the 11thembodiment of the present invention can be applied;

FIG. 28 is a schematic sectional view showing an example of the printershown in FIG. 27;

FIG. 29 is a block diagram showing an arrangement of a printer and avideo interface which connects the video controller and printer engineshown in FIG. 27;

FIG. 30 is a block diagram showing an arrangement of the videocontroller shown in FIG. 27;

FIG. 31 is a flow chart showing an example of data processing proceduresaccording to the 11th embodiment;

FIG. 32 is a view showing an example of a double-sided printing sequencepattern in the printer according to the 11th embodiment;

FIG. 33 is a view for explaining a print mode switching sequence statein the printer according to the 11th embodiment;

FIGS. 34 to 37 are timing charts for explaining a print data processingstate according to the 11th embodiment;

FIG. 38 is a flow chart showing an example of data processing proceduresaccording to the 12th embodiment;

FIG. 39 is a view for explaining a print mode switching sequence stateaccording to, the 12th embodiment; and

FIG. 40 is a view for explaining the memory map of a storage mediumwhich stores various data processing programs readable by the printeraccording to the 11th embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

The first embodiment will be described in detail below with reference tothe accompanying drawings by applying this embodiment to a laser beamprinter (to be simply referred to as an LBP hereinafter).

FIG. 1 is a sectional view showing the internal structure of the LBPaccording to the first embodiment of the present invention.

In FIG. 1, reference numeral 100 denotes an LBP main body. The LBP 100creates character patterns, graphic patterns, images, and the like inaccordance with character print instructions, various graphic drawinginstructions, image drawing instructions, color designationinstructions, and the like supplied from a terminal computer 201 (FIG.2) connected to a LAN 214 (FIG. 2), and forms an image on a print sheetserving as a print medium. Reference numeral 151 denotes an operationpanel on which switches for user operation, an LED display fordisplaying the state of the LBP 100, an LCD display, and the like arearranged; and 101, a printer controller which controls the operation ofthe whole LBP 100 and analyzes a character print instruction and thelike supplied from the terminal computer 201.

The LBP 100 according to the first embodiment comprises imageforming/developing mechanisms for forming M (Magenta), C (Cyan), Y(Yellow), and K (blacK) images in order to convert pieces of R, G, and Bcolor information into pieces of M, C, Y, and K color information andparallel-form/develop images corresponding to the pieces of colorinformation. The printer controller 101 generates M, C, Y, and K printimages, generates video signals corresponding to the print images, andoutputs the signals to M, C, Y, and K laser drivers 110, 120, 130, and140.

The M (Magenta) laser driver 110 is a driver circuit for driving asemiconductor laser 111, and ON/OFF-switches a laser beam 112 emitted bythe semiconductor laser 111 in accordance with an input video signal.The laser beam 112 is oscillated right and left by a rotary polygonmirror 113 to scan the surface of an electrostatic drum 114. As aresult, the electrostatic latent image of a character or graphic patternis formed on the electrostatic drum 114. The electrostatic latent imageis developed on the drum 114 by a developing unit (toner cartridge) 115arranged around the electrostatic drum 114, and the toner image istransferred from the drum onto a print sheet.

As for C (Cyan), Y (Yellow), and K (blacK), identical imageforming/developing mechanisms are employed. The C (Cyan) imageforming/developing mechanism comprises the laser driver 120, asemiconductor laser 121, a laser beam 122, a rotary polygon mirror 123,an electrostatic drum 124, and a developing unit 125. The Y (Yellow)image forming/developing mechanism comprises the laser driver 130, asemiconductor laser 131, a laser beam 132, a rotary polygon mirror 133,an electrostatic drum 134, and a developing unit 135. The K (blacK)image forming/developing mechanism comprises the laser driver 140, asemiconductor laser 141, a laser beam 142, a rotary polygon mirror 143,an electrostatic drum 144, and a developing unit 145. Each image formingfunction is the same as the M (Magenta) image forming/developingmechanism, and a description thereof will be omitted.

The LBP 100 has two modes: monochrome and full-color print processes.The K (blacK) electrostatic drum 144 is fixed, whereas the M (Magenta),C (Cyan), and Y (Yellow) electrostatic drums 114, 124, and 134 arevertically movable in FIG. 1. In the monochrome print process, theelectrostatic drums 114, 124, and 134 are retracted to positionsslightly apart from a sheet convey belt 107 in order to avoid the wearbetween the sheet convey belt 107 and the electrostatic drums 114, 124,and 134. Retraction and return operations take about 5 sec each, andprinting of a succeeding sheet delays in switching from the color printprocess to the monochrome print process and vice versa.

The print sheet is a cut sheet. A plurality of cut sheets are stored ina sheet cassette 102 mounted in the LBP 100, and held at a predeterminedlevel within the cassette 102 by a spring 103. A sheet is fed from thesheet cassette 102 into the apparatus by rotation of a pickup roller 104and convey rollers 105 and 106, set on the sheet convey belt 107, andpasses through the M, C, Y, and K image forming/developing mechanisms,transferring images corresponding to the respective colors. Referencenumeral 102-2 denotes a second sheet cassette; 103-2, a spring accessoryto the second sheet cassette 102-2; 104-2, a pickup roller; and 105-2, aconvey roller. The arrangement of the second sheet cassette 102-2 iscompletely the same as that of the sheet cassette 102.

M, C, Y, and K toners (ink powders) transferred onto the print sheet arefixed onto the print sheet by the heat and pressure of a fixing unit108. The print sheet on which the image is transferred, printed, andfixed is discharged to the upper portion of the apparatus main body ofthe LBP 100 by convey rollers 109 and 150.

FIG. 2 is a block diagram showing the schematic arrangement of thecontroller 101 of the LBP according to the first embodiment.

The controller 101 of the LBP receives data containing character,graphic, and image drawing instructions, color information, and the likesent from the terminal computer 201 via the LAN 214, and prints documentinformation and the like for each page. Reference numeral 202 denotes anI/O interface which exchanges various pieces of information with theterminal computer 201; 203, an input buffer which temporarily storesvarious pieces of information input via the I/O interface 202; and 204,a character pattern generator which comprises a font information unit218 for storing attributes such as a character width and height and theaddress of an actual character pattern, a character pattern unit 219 forstoring character patterns, and a read control program. The read controlprogram is stored in a ROM 215, and has a code conversion function of,when receiving a character code, calculating the address of a characterpattern corresponding to the character code.

Reference numeral 205 denotes a RAM which contains a font cache area 207for storing a character pattern output from the character patterngenerator 204, and a storage area 206 for storing an external characterfont, current printing environment, and the like sent from the terminalcomputer 201. In this manner, pattern information temporarily mappedinto a character pattern is stored in the font cache area 207 serving asa font cache. This eliminates the need for decoding the same characteragain and mapping it into a pattern when printing the same character.The mapping speed to a character pattern increases.

A CPU 208 controls the overall printer controller, and controls thewhole operation of the LBP 100 in accordance with the control program ofthe CPU 208 that is stored in the ROM 215. Reference numeral 209 denotesan intermediate buffer which holds a group of internal intermediate datagenerated based on input data. After data of one page are received,converted into simpler intermediate data, and stored in the intermediatebuffer 209, the intermediate data are rendered by a renderer 210 foreach band, and output as a print image to a band buffer 211. The bandbuffer 211 can store print images of at least eight bands. A print imageoutput to the band buffer 211 is converted into a video signal by anoutput interface 212, and output to a printer 213. The printer 213 isthe printing mechanism of a page printer which prints image informationbased on a video signal from the output interface 212.

The LBP of the first embodiment described above with reference to FIG. 1parallel-executes formation and development of M, C, Y, and K images.For this purpose, the output interface 212 comprises four interfaces: M,C, Y, and K output interfaces. These interfaces independently read outdot data from the band buffer 211, convert them into video signals, andoutput the signals to the laser drivers 110, 120, 130, and 140 of therespective planes.

The intermediate buffer 209 can store intermediate data of a pluralityof pages. Processing subsequent to read and rendering is performed insynchronism with the operation of the printer 213 serving as theprinting mechanism.

Reference numeral 216 denotes a nonvolatile memory formed from a generalEEPROM or the like, and will be referred to as an NVRAM (Non VolatileRAM) hereinafter. The NVRAM 216 stores, e.g., panel setting valuesdesignated on the operation panel 151.

The ROM 215 includes analysis of data input from the terminal computer201, generation of intermediate data, the control program of the printer213, and a color conversion table from an RGB color space into an MCYKcolor space. Reference numeral 220 denotes a hard disk which can storearbitrary information and does not loose information even uponpower-off.

The structure of intermediate data generated by the intermediate buffer209 in the first embodiment will be explained with reference to FIG. 3.

FIG. 3 shows a data format representing the data structure ofintermediate data.

In FIG. 3, intermediate data 300 represents intermediate data of onepage generated within the intermediate buffer 209, and contains a header310 and drawing object area 320. At the start of generating intermediatedata of a page, only the header 310 is acquired, and no drawing objectarea 320 exists. The drawing object area 320 is a variable-length areawhich is extended every time a drawing object is added.

An area 311 of the header 310 is a flag area representing whether thepage is being generated or has been generated. “0” meaning “duringgeneration” is set in the flag area in the initial state, and “1”meaning “completion of generation” is set upon the completion ofgenerating intermediate data of a page. An area 312 represents a sheetsize, and information representing a sheet size such as “A3” or “A4” isset. An area 313 is a sheet type information area representing the typeof paper, and sheet type information such as “plain paper”, “thickpaper”, or “OHP” is set. An area 314 is a page color information arearepresenting whether the page is a monochrome page or full-color page.“0” meaning “undefined” is set in the area 314 in the initial state.Every time a drawing object is added to the drawing object area 320, “1”meaning “full color” is set when the object is a full-color drawingobject. If the value of the area 314 is kept “0” (“undefined”) upon thecompletion of generating intermediate data of the page, “2” meaning“monochrome” is set. An area 315 is a print process color informationarea representing a print process when printing a page. “0” meaning“undefined” is set in the area 315 in the initial state. If the area 314holds “1” meaning “full color” upon the completion of generatingintermediate data of the page, “1” representing “full-color printprocess” is also set in the area 315. If the page is a monochrome page,i.e., “2” representing “monochrome” is set in the area 314, no printprocess is decided upon the completion of generating intermediate data,and “0” meaning “undefined” is kept set in the print process colorinformation area 315.

The processing procedures of intermediate data generation processingwill be described in more detail with reference to the flow chart ofFIG. 4.

FIG. 4 is a flow chart showing intermediate data generation processingin the LBP 100 according to the first embodiment. A program whichexecutes this processing is stored in the ROM 215.

After generation of intermediate data 300 of a given page starts, theheader area 310 is ensured in step S401. The flow shifts to step S402 toset, in the area 311, “0” meaning that the intermediate data is beinggenerated. In steps S403 and S404, a sheet size and sheet typedesignated by commands are set. Note that the sheet size and sheet typehave already been decided at the start of generating intermediate dataof the page.

In steps S405 and S406, “undefined” is set in the page color informationarea 314 and print process color information area 315. By theseprocesses, initial setting of the header 310 is completed, and the flowshifts to drawing command processing.

One command is interpreted in step S407, and the flow advances to stepS408 to check whether the command is a page end command or a drawingcommand for a general character, graphic, image, or the like. For thedrawing command, the flow shifts to step S409 to process the drawingcommand and add the drawing object to the drawing object area 320. Notethat the drawing object area 320 is extended, as needed. After thedrawing object is added, the flow shifts to step S410 to check whetherthe drawing object is a color drawing object. If YES in step S410, theflow shifts to step S411 to set “full color” in the page colorinformation area 314, and returns to step S407 to process the nextcommand. If NO in step S410, the flow directly returns to step S407.

If the command is a page end command in step S408, the flow advances tostep S412 to check whether “full color” has been set in the page colorinformation area 314. If YES in step S412, the flow advances to stepS413 to set “full color” also in the print process color informationarea 315. If NO in step S412, the flow shifts to step S414 to change thepage color information area 314 to “monochrome”. After step S413 or S414is executed, the flow shifts to step S415 to set, in the area 311, “1”meaning the completion of generating intermediate data, and intermediatedata generation processing ends.

After intermediate data of one page has been generated, intermediatedata of the next page is subsequently generated. Intermediate data of aplurality of pages are stored in the intermediate buffer 209.

After intermediate data of at least one page is stored in theintermediate buffer 209, the page can be printed. A sheet size, sheettype, and print process type (monochrome/full color) are designated withrespect to the printer (printing mechanism) 213, and a print request isissued. When the printer 213 becomes ready, intermediate data in theintermediate buffer 209 is rendered for each band in synchronism withsheet convey in the printer 213. Dot data is converted into a videosignal, which is transferred to the printer 213.

Whether to select the monochrome print process or full-color printprocess complies with the print process color information 315. Formonochrome page printing, which of the print processes is to be selectedis not determined on the intermediate data generation stage, and isdecided immediately before issuing a print request to the printer 213.

Features according to the first embodiment will be briefly explainedprior to a detailed description of processing in the first embodiment.

(1) For monochrome page printing, decision of the print process dependson the presence/absence of an immediately preceding page, or temporalcontinuity with the immediately preceding page, and the print process ofthe immediately preceding page. For example, when the immediatelypreceding page is printed in the monochrome print process and a targetpage is to be successively printed, the monochrome print process is keptselected without switching the print process. When no immediatelypreceding page exists, the immediately preceding page and target pageare not successive, or the immediately preceding page is printed in thefull-color print process, the print process of the target page is notdecided from only the above-mentioned determination information.

(2) The print process is determined based on the number of succeedingpages and attributes representing whether these pages are monochrome orfull-color pages. These pieces of information are used when the printprocess of monochrome printing cannot be decided from the determinationinformation described in (1). For example, if no full-color page appearsamong N pages subsequent to a target page, the target page is printed inthe monochrome print process. Note that N is an integer of 1 or more,and this value may be an optimal one corresponding to the printingmechanism or set in advance on the operation unit 151. If no succeedingpage is generated, whether a succeeding page is being generated ischecked, and if so, the start of printing a target page may be delayedwithin a given range.

(3) The print process is determined based on the difference in sheetsize or sheet type between an immediately preceding page and a targetpage. This is because a general printing apparatus takes a longerinterval than a general print processing interval when switching thesheet size or sheet type. For example, in a general laser beam printer,the print process for a thick sheet or OHP sheet becomes slower thanthat for a plain sheet in order to increase the fixation of toner(powder ink). To switch the process speed, the next sheet is not feduntil an immediately preceding sheet is completely discharged outsidethe apparatus. In this case, switching between the full-color andmonochrome print processes hardly decreases the speed. Thus, the printprocess is decided in consideration of determination information (3) inaddition to (1) and (2) described above. For example, if an immediatelypreceding page is printed in the full-color print process, a target pageis a monochrome page, and no subsequent page exists, the target page isprinted in the full-color print process in consideration of onlydetermination information (1) or (2). However, by taking determinationinformation (3) into consideration, the monochrome print process isselected even when an immediately preceding page is printed on, e.g., anOHP sheet, a target page is printed on a plain sheet, and the colorprint process is determined based on condition (1) or (2).

In this fashion, the first embodiment aims to minimize a decrease inprinting speed caused by switching of the print process, and at the sametime realize power saving and reduction in load on the printingmechanism by intelligently deciding the print process of a monochromepage.

Print process selection processing for a monochrome page as a feature ofthe first embodiment will be explained.

As described above, the LBP 100 according to the first embodiment hasmonochrome and full-color print processes. The monochrome print processadvantageously has higher speed, lower power, and a smaller load on theprinting mechanism in comparison with the full-color print process.

However, a loss time of about 5 sec is generated for retracting theabove-mentioned drum in switching the print process from the monochromeprint process to the full-color print process and vice versa. Note thatno print process switching time is generated when printing starts from aprint process OFF state or a target page is not successively printedwith a printing time interval from an immediately preceding page due toany reason, because switching, of the print process is completed until acut sheet is fed from the sheet cassette 102 and reaches the imageforming/developing mechanism.

The printing speed is 30 pages/min for the monochrome print process and20 pages/min for the full-color print process.

The processing procedures of print process selection processing for amonochrome page will be described with reference to FIGS. 5A and 5Bunder these conditions.

FIGS. 5A and 5B are flow charts for mainly explaining the print processof a monochrome page in the LBP 100 according to the first embodiment.

In step S501, whether a page to be printed is monochrome or full-coloris checked. This can be determined by referring to the page colorinformation 314. For a full-color page, the flow shifts to step S502 toselect the full-color print process, and print process selectionprocessing for the target page ends. In this case, “full color” is setin the print process color information 315 during generation ofintermediate data, and “full color” need not be set again in the printprocess color information 315.

If the page is a monochrome page in step S501, the flow advances to stepS503 to check whether an immediately preceding page exists. Intermediatedata of a given page is deleted when printing of the page is completed,i.e., when the page is printed and a page-printed sheet is dischargedoutside the apparatus. Before this, the contents of the intermediatebuffer for this page are held. Thus, the presence/absence of animmediately preceding page can be determined from the presence/absenceof intermediate data of the immediately preceding page. If YES in stepS503, the flow advances to step S504 to check whether the print processof the page is the monochrome print process. The print process of theimmediately preceding page has been determined at this time, and set inthe print process color information 315 of the intermediate data. If theprint process of the immediately preceding page is the monochrome printprocess, the flow shifts to step S505 to select the monochrome printprocess, and then processing ends. At this time, “monochrome” is set inthe print process color information 315.

If no immediately preceding page exists in step S503, or if the printprocess of the immediately preceding page is determined in step S504 tobe the full-color print process, the print process of the target page isdecided using the presence/absence of a succeeding page and the pagecolor information 314 as pieces of determination information. In thefirst embodiment, the number of succeeding pages to be referred to is“1” or “2”. The number of pages to be referred to will be represented byN.

If NO in step S503, the flow shifts to step S506 to set “1” as thenumber N of succeeding pages to be referred to, and shifts to step S508.If the print process of the immediately preceding page is determined instep S504 to be “full color”, the flow advances to step S507 to set “2”as the number N of succeeding pages to be referred to, and shifts tostep S508. This means that a larger number of succeeding pages arereferred to in the presence of an immediately preceding page whose printprocess is “full color” than in the absence of any immediately precedingpage. In this case, the print process is controlled not to be switchedto the monochrome print process unless a larger number of monochromepages continue. This is because in the presence of an immediatelypreceding page whose print process is “full color”, switching to themonochrome print process requires a loss time of about 5 sec owing tomovement of the drum or the like as described.

After the number N of pages to be referred to is decided in step S506 orS507, the flow shifts to step S508 to reset the timer. In the firstembodiment, the flow waits for generation of a succeeding page if theprint process of a target page cannot be decided owing to a small numberof succeeding pages. The timer controls to prevent the standby time fromexceeding a predetermined time.

The flow shifts to step S509 to check whether N or more succeeding pagesexist. This can be determined from the number of intermediate datastored in the intermediate buffer 209. If YES in step S509, the flowshifts to step S510 to check whether the N succeeding pages contain afull-color page. If YES in step S510, the flow advances to step S511 toselect the full-color print process, and then processing ends. At thistime, “full color” is set in the print process color information 315. IfNO in step S510, the flow shifts to step S512 to select the monochromeprint process, and then processing ends.

If NO in step S509, the flow advances to step S513 to check whether afull-color page appears among succeeding pages. If YES in step S513, theflow advances to step S514 to select the full-color print process, andthen processing ends. At this time, “full color” is set in the printprocess color information 315. If NO in step S513, the flow advances tostep S515.

In step S515, the presence of a page which is being generated ischecked. This can be determined by referring to the header 310 of thenewest intermediate data in the intermediate buffer 209 and checkingwhether “during generation” is set in the area 311. If NO in step S515,the flow shifts to step S516 to select the monochrome print process, andthen processing ends.

If YES in step S513, the flow shifts to step S517 to check whether thetimer has started. If NO in step S517, the flow shifts to step S518 tostart the timer, and returns to step S509 to check again whether N ormore succeeding pages exist. If YES in step S517, the flow shifts tostep S519 to check whether a predetermined time has elapsed. In thefirst embodiment, the predetermined time is 2 sec at maximum. If YES instep S519, the flow shifts to step S516 to select the monochrome printprocess, and then processing ends. If NO in step S519, the flow returnsto step S509 to check again whether N or more succeeding pages exist.

The above-described print process selection processing for a monochromepage in the first embodiment can realize switching to an optimal printprocess in accordance with the presence/absence of pages before andafter a page to be printed, the print processes of preceding andsucceeding pages, and whether preceding and succeeding pages arecolor/monochrome pages.

Second Embodiment

In the first embodiment, the print process of a page to be printed isdecided by giving attention to the presence/absence of pages before andafter the page to be printed, the print processes of preceding andsucceeding pages, and whether preceding and succeeding pages arecolor/monochrome pages. In the second embodiment, a more efficient printprocess is selected in consideration of switching of the sheet size orsheet type. As an example of changing the print process depending on thesheet size or sheet type, when data is printed on a thick sheet or OHPsheet, the sheet convey speed is decreased and the heating time by thefixing unit is prolonged for higher toner fixation.

An LBP 100 according to the second embodiment can print data on a plainsheet, thick sheet, or OHP sheet, and can be applied to an LBP with aprinting mechanism having different convey speeds.

The internal structure of the LBP 100 and the arrangement of thecontroller in the second embodiment are the same as those described inthe first embodiment with reference to FIGS. 1 and 2, and a descriptionthereof will be omitted. The structure of intermediate data generated inan intermediate buffer 209 and the processing procedures of generationprocessing are also the same as those described in the first embodimentwith reference to FIGS. 3 and 4, and a description thereof will beomitted.

In switching the sheet convey speed, an LBP of this type generallydischarges all sheets during conveyance outside the apparatus, and thenswitches the rotational speeds of various sheet convey rollers androtary polygon mirrors. To print a monochrome page on a plain sheetsubsequently to printing of an OHP sheet in the full-color printprocess, a plain sheet cannot be fed until the immediately precedingpage is discharged outside the apparatus. Hence, even if a monochromepage is printed by switching from the full-color print process to themonochrome print process, the necessary time does not surface.

The processing procedures of print process selection processing for amonochrome page in consideration of the characteristics of the printingmechanism will be described with reference to FIGS. 6A and 6B.

FIGS. 6A and 6B are flow charts showing the processing procedures ofprint process selection processing for a monochrome page in the LBP 100according to the second embodiment of the present invention.

In step S601, whether a page to be printed is monochrome or full-coloris checked. This can be determined by referring to page colorinformation 314 of intermediate data. For a full-color page, the flowshifts to step S602 to select the full-color print process, and printprocess selection processing for the page to be printed ends. In thiscase, “full color” is set in print process color information 315 duringgeneration of intermediate data, and need not be set again in the printprocess color information 315.

If the page is a monochrome page in step S601, the flow advances to stepS603 to check whether an immediately preceding page exists and the pageis of the same sheet type as the page to be printed. Since intermediatedata is deleted when printing of a page is completed, thepresence/absence of an immediately preceding page can be determined fromthe presence/absence of intermediate data of the immediately precedingpage. The sheet type can be determined from sheet type information setin a sheet type area 313 of a header 310 of intermediate data. Note thatdifferent sheet types mean different print processes, like an OHP sheetand plain sheet.

If the immediately preceding page exists in step S603 and the page is tobe printed on a sheet of the same type as the page to be printed, theflow advances to step S604 to check whether the print process of thepage is the monochrome print process. The print process of theimmediately preceding page has been determined at this time, and set inthe print process color information 315 of the intermediate data of theimmediately preceding page. If the print process of the immediatelypreceding page is determined to be the monochrome print process byreferring to the print process color information 315, the flow shifts tostep S605 to select the monochrome print process, and then processingends. At this time, “monochrome” is set in the print process colorinformation 315.

If no immediately preceding page exists in step S603, if the printprocess of the immediately preceding page is the full-color printprocess in step S604, or if the sheet type is different in step S603,the print process of a monochrome page to be printed is decided usingthe presence/absence of a succeeding page, the page color information314, and the sheet type information 313 as pieces of determinationinformation. In the second embodiment, the number of succeeding pages tobe referred to is “1” or “2”. The number of pages to be referred to willbe represented by N.

If no immediately preceding page exists in step S603 or the sheet typeis different, the flow shifts to step S606 to set “1” as the number N ofsucceeding pages to be referred to, and shifts to step S608. If theprint process of the immediately preceding page is determined in stepS604 to be “full color”, the flow advances to step S607 to set “2” asthe number N of succeeding pages to be referred to, and shifts to stepS608. This means that a larger number of succeeding pages are referredto in the presence of an immediately preceding page whose print processis “full color” than in the absence of any immediately preceding page orwhen the sheet type is different and the target page cannot be fed untilthe immediately preceding page is discharged outside the apparatus. Whenan immediately preceding page whose print process is “full color”exists, the print process is controlled not to be switched to themonochrome print process unless a larger number of monochrome pagescontinue. This is because in the presence of an immediately precedingpage whose print process is “full color”, switching to the monochromeprint process requires a loss time of about 5 sec, as described.

After the number N of pages to be referred to is decided in step S606 orS607, the flow shifts to step S608 to reset the timer. In the secondembodiment, the flow waits for generation of a succeeding page if theprint process of a monochrome page to be printed cannot be decided owingto a small number of succeeding pages. The timer controls to prevent thestandby time from exceeding a predetermined time.

The flow shifts to step S609 to check whether N or more succeeding pagesexist. This can be determined from the number of intermediate datastored in the intermediate buffer 209. If YES in step S609, the flowshifts to step S610 to check whether the N succeeding pages contain afull-color page and whether the sheet type changes. If the N succeedingpages contain a full-color page and the sheet type does not change, theflow advances to step S611 to select the full-color print process, andthen processing ends. At this time, “full color” is set in the printprocess color information 315.

If the N succeeding pages do not contain a full-color page or the sheettype changes in step S610, the flow shifts to step S612 to select themonochrome print process, and then processing ends.

If NO in step S609, the flow advances to step S613 to check whether thesheet type changes. If YES in step S613, the flow advances to step S614to select the monochrome print process, and then processing ends.

If NO in step S613, the flow shifts to step S615 to check whether afull-color page appears among succeeding pages. If YES in step S615, theflow advances to step S616 to select the full-color print process, andthen processing ends. At this time, “full color” is set in the printprocess color information 315.

If NO in step S615, the flow advances to step S617 to check the presenceof a page which is being generated. This can be determined by referringto the header 310 of the newest intermediate data in the intermediatebuffer 209 and checking whether “during generation” is set in the area311. If NO in step S617, the flow shifts to step S618 to select themonochrome print process, and then processing ends.

If YES in step S617, the flow shifts to step S619 to check whether thetimer has started. If NO in step S619, the flow shifts to step S620 tostart the timer, and returns to step S609 to check again whether N ormore succeeding pages exist. If YES in step S619, the flow shifts tostep S621 to check whether the timer has counted a predetermined time.In the second embodiment, the predetermined time is 2 sec at maximum. IfYES in step S621, the flow shifts to step S618 to select the monochromeprint process, and then processing ends. If NO in step S621, the flowreturns to step S609 to check again whether N or more succeeding pagesexist and execute the same processing as that described above.

The above-described print process selection processing for a monochromepage in the second embodiment can realize switching to an optimal printprocess corresponding to the characteristics of the printing mechanismin consideration of the presence/absence of pages before and after apage to be printed, the print processes of these pages, thecolor/monochrome attribute, and switching of the sheet type.

The second embodiment adopts the sheet type as a sheet attribute. For aprinting mechanism which cannot perform continuous printing due toswitching of the sheet size, a print process may be selected byreferring to the sheet size in addition to the sheet type.

The number (N) of succeeding pages to be referred to may be designatedfrom an operation panel 151 or a printer driver (not shown).

As described above, according to the first and second embodiments, anoptimal print process can be selected in consideration of whether animmediately preceding page exists, in addition to the conventionalmethod of deciding a print process for printing a monochrome page inconsideration of whether immediately preceding and succeeding pages aremonochrome or full-color.

For a printing mechanism in which the time taken to switch between themonochrome and full-color print processes does not surface when thesheet attribute such as the sheet type or sheet size is switched, anoptimal print process can be selected in consideration of thecharacteristics of the printing mechanism.

As described above, the present invention can more efficiently decidethe print process of a monochrome page, and prevent a print processingdelay and the wear of a device.

Also, the present invention can further optimize decision of the printprocess by determining the print process of a monochrome page on thebasis of not whether a page to be printed is monochrome or full-color,but the presence/absence of immediately preceding and succeeding pagesand their attributes.

Third Embodiment

The third embodiment provides a means for realizing optimization of theprint process by user operation when two print processes are differentin processing speed and a predetermined time is required to switch theprint process in a printing system which is constituted by a full-colorprinter having monochrome and full-color print processes and its printerdriver.

The internal structure of an LBP 100 and the arrangement of thecontroller in the third embodiment are the same as those described inthe first embodiment with reference to FIGS. 1 and 2, and a descriptionthereof will be omitted. The structure of intermediate data generated inan intermediate buffer 209 is also the same as that described in thefirst embodiment with reference to FIG. 3, and a description thereofwill be omitted.

In the full-color print process, an image can be formed by all C, M, Y,and K drums. To print monochrome data in this print process, an image isactually formed by only a K electrostatic drum 144. In the monochromeprint process, three drums corresponding to C, M, and Y move to retractpositions. While a print sheet passes through these three drums, theprint sheet is conveyed at a higher speed than in general imageformation.

In the third embodiment, an area 315 is a print process colorinformation area representing a print process when printing a page. “0”meaning “undefined” is set in the area 315 in the initial state. If anarea 314 holds “1” meaning “full color” upon the completion ofgenerating intermediate data of the page, “1” representing “full-colorprint process” is also set in the area 315. If the page is a monochromepage, i.e., “2” representing “monochrome” is set in the area 314, “1”representing “full-color print process” or “2” representing “monochromeprint process” is set in accordance with print mode information (set bythe user as will be described later) added to a print job.

The processing procedures of intermediate data generation processingwill be described in more detail with reference to the flow charts ofFIGS. 7A and 7B.

After generation of intermediate data 300 of a given page starts, aheader area 310 is ensured in step S1401, and “0” meaning that theintermediate data is being generated is set in an area 311 in stepS1402. In steps S1403 and S1404, a sheet size and sheet type designatedby commands are set. Note that the sheet size and sheet type havealready been decided at the start of generating intermediate data of thepage. In steps S1405 and S1406, “undefined” is set in the page colorinformation area 314 and print process color information area 315.

By these processes, initial setting of the header 310 is completed, andthe flow shifts to drawing command processing.

One command is interpreted in step S1407, and whether the command is apage end command or a drawing command for a general character, graphic,image, or the like is checked in step S1408.

For the drawing command, the flow shifts to step S1409 to process thedrawing command and add the drawing object to a drawing object area 320.Note that the drawing object area 320 is extended, as needed. After thedrawing object is added, the flow shifts to step S1410 to check whetherthe drawing object is a color drawing object. If YES in step S1410,“full color” (“1”) is set in the page color information area 314 in stepS1411. The flow returns to step S1407 to process the next command. If NOin step S1410, the flow directly returns to step S1407.

If the command is a page end command, the flow advances from step S1408to step S1412 to check whether “full color” has been set in the pagecolor information area 314. If YES in step S1412, the flow advances tostep S1413 to set “full color” (“1”) also in the print process colorinformation area 315.

If NO in step S1412, the flow shifts to step S1414 to change the pagecolor information area 314 to “monochrome” (“2”). In step S1415, printmode information added to the start of print data of a print job is readout, and whether the print mode information represents“monochrome/full-color switching mode” or “fixed full-color mode” isdetermined.

To select “monochrome/full-color switching mode”,#PROCESS−COLOR=AUTOis designated at the start of print data of a print job. To select“fixed full-color mode”,#PROCESS−COLOR=FULLCOLORis designated. If no print mode information is designated at the startof a print job, “monochrome/full-color switching mode” is set.

For “fixed full-color mode”, the flow advances from step S1415 to stepS1413 to set “full color” in the print process color information area315. For “monochrome/full-color switching mode”, the flow shifts fromstep S1415 to step S1416 to set “monochrome” in the print process colorinformation area 315.

“1” meaning the completion of generating intermediate data is set in thearea 311 in step S1417, and intermediate data generation processingends.

After intermediate data of one page has been generated, intermediatedata of the next page is subsequently generated. Intermediate data of aplurality of pages are stored in the intermediate buffer 209.

After intermediate data of at least one page is stored in theintermediate buffer 209, the page can be printed. A sheet size, sheettype, and print process type (monochrome/full color) are designated withrespect to a printing mechanism 213, and a print request is issued. Whenthe printing mechanism 213 becomes ready, intermediate data in theintermediate buffer 209 is rendered for each band in synchronism withsheet convey at the printing mechanism 213. Dot data is converted into avideo signal, which is transferred to the printing mechanism 213.Whether to select the monochrome print process or full-color printprocess complies with the print process color information 315.

The printing execution window of the printer driver and a selected printmode will be described with reference to FIG. 8.

Reference numeral 500 denotes a printing execution instruction window bythe printer driver. A field 501 is used to designate a processingresolution in printing a document, and “fine” or “quick” is exclusivelyselected. Note that print processing is done at 600 dpi for “fine” and300 dpi for “quick”. In FIG. 8, “fine” is selected.

A field 502 is used to designate whether to print a document in fullcolor or monochrome, and “full-color printing” or “automatic switchingprinting” is exclusively selected. In FIG. 8, “full-color printing” isselected.

Set values designated in the fields 501 and 502 are transmitted asadditional information of print data to the LBP 100 by clicking aprinting execution button 503.

Header information added to print data is parenthesized between“{ec}%-HEADER” and “{ec}%-END”. For example, when “resolution=fine” and“color=full-color printing” are set, header information:

-   {ec}%-HEADER-   #RESOLUTION=FINE-   #PROCESS−COLOR=FULLCOLOR-   {ec}%-END    is added. Note that {ec} represents hexadecimal 1B.

In this case, #PROCESS−COLOR=FULLCOLOR means “fixed full-color mode”.

When “automatic switching printing” is selected in the field 502, headerinformation:#PROCESS−COLOR=AUTOis added, which means “monochrome/full-color switching mode”. In thiscase, a monochrome page is printed in the monochrome print process, anda full-color page is printed in the full-color print process.

By clicking a cancel button 504, the printing window 500 is closedwithout executing printing.

According to the above-described print process selection processing inthe third embodiment, a print mode in which printing is performed in thefull-color print process can be selected regardless of whether a page tobe printed is monochrome or full-color. When this print mode isselected, frequent switching of the print process can be prevented evenfor a print job in which full-color and monochrome pages alternatelyexist. As a result, high-speed print processing with low powerconsumption can be realized.

Fourth Embodiment

In full-color printing according to the third embodiment, all pages areprinted in the full-color print process. For a document in which manymonochrome pages successively appear, this may be disadvantageous interms of the printing speed, the load on the printing mechanism, andpower consumption in comparison with a case wherein a monochrome page isprinted by switching the print process to the monochrome print process.A typical example is a document in which only the first page isfull-color and several ten remaining pages are monochrome.

To avoid this, the printing execution instruction window of the thirdembodiment is modified to allow the user to select a setting suitablefor printing of a document containing many monochrome pages.

The internal structure of an LBP and the arrangement of the controllerin the fourth embodiment are the same as those described in the firstembodiment with reference to FIGS. 1 and 2, and a description thereofwill be omitted. The structure of intermediate data generated in anintermediate buffer 209 and the processing procedures of generationprocessing are also the same as those described in the third embodimentwith reference to FIG. 3 and FIGS. 7A and 7B, and a description thereofwill be omitted.

The printing execution window of the printer driver and a selected printmode will be described with reference to FIG. 9.

Reference numeral 600 denotes a printing execution instruction window bythe printer driver. A field 601 is used to designate a processingresolution in printing a document, similar to the field 501 of the thirdembodiment.

A field 602 is used to designate whether to print a document in fullcolor or monochrome, and “full-color printing”, “monochrome printing”,or “automatic switching printing” is exclusively selected. In FIG. 9,“full-color printing” is selected.

Set values designated in the fields 601 and 602 are transmitted asadditional information of print data to an LBP 100 by clicking aprinting execution button 603. The structure of header information addedto print data is the same as that in the third embodiment exceptdesignation of “#PROCESS-COLOR” in the field 602.

When “full-color printing” is selected in the field 602, headerinformation:#PROCESS−COLOR=FULLCOLORis added, which means the above-mentioned “fixed full-color mode”. Sinceall pages are printed in the full-color print process, this mode issuitable for outputting a document containing not so many monochromepages.

When “monochrome printing” is selected in the field 602, headerinformation:#PROCESS−COLOR=AUTOis added, which means “monochrome/full-color switching mode”. Since theprinter driver generates monochrome print data regardless of whetheroriginal data is color or monochrome, all pages are printed in themonochrome print process.

When “automatic switching printing” is selected in the field 602, headerinformation:#PROCESS−COLOR=AUTOis added, which means “monochrome/full-color switching mode”. This modeis suitable for outputting a document containing many monochrome pagesbecause a monochrome page is printed in the monochrome print process anda full-color page is printed in the full-color print process.

By clicking a cancel button 604, the printing window 600 is closedwithout executing printing.

According to the above-described print process selection processing inthe fourth embodiment, it can be set to print all pages in thefull-color print process when printing a document having a relativelysmall number of monochrome pages. It can also be set to print all pagesin the monochrome print process when printing a document having manymonochrome pages. That is, the user can freely select a print modesuitable for the feature of a document.

As described above, according to each of the above embodiments, allpages can be set to be printed in the full-color print process. If thismode is set for a full-color print job containing a relatively smallnumber of monochrome pages, the switching time, power consumption, andload on the printing mechanism by print process switching operation canbe reduced.

A print process for printing a monochrome page is decided in accordancewith the printing condition of the printer driver UI. The printer neednot wait for generation of intermediate data of a succeeding page, andcan start printing at the same time as generation of intermediate dataof a target page.

Note that the print process decision method (method of deciding a coloror monochrome process) described in the first and second embodiments maybe applied to “automatic switching printing” in the third and fourthembodiments.

As described above, the present invention allows the user to set adesired print mode in which data is printed in the full-color printprocess regardless of whether an object to be printed is monochrome orfull-color, and can easily realize optimization of a print processcorresponding to a print job.

Fifth Embodiment

An arrangement of a color laser beam printer will be described as anexample of an output apparatus according to the fifth embodiment.

FIG. 10 is a block diagram showing a printing system to which the fifthembodiment is applied, i.e., showing a system configuration constitutedby a host computer 1001, a color laser beam printer 1030, a network 1002connected to these devices, and communication lines 1003 and 1004 forconnection to the network 1002.

In the color laser beam printer 1030, reference numeral 1031 denotes alaser beam printer controller (to be referred to as a controllerhereinafter) which controls the whole operation of the printer 1030.

In the controller 1031, reference numeral 1032 denotes an I/O unit whichhas a function of inputting/outputting data via the communication line1004 connected to the network 1002. Communication with each terminaldevice is done via the I/O unit 1032, communication line 1004, andnetwork 1002. Reference numeral 1033 denotes an I/O buffer used totransmit/receive printing control codes, control codes for registeringvarious pieces of information in a server terminal, and data from eachcommunication means; 1034, a CPU which controls the overall operation ofthe controller; 1035, a program ROM which stores a program describingthe operation of the CPU 1034; 1036, a RAM used as a work memory forperforming analysis of control codes and data, calculation necessary forprinting, and processing of print data; and 1048, a nonvolatile RAM(NVRAM) which stores data that must be held even upon power-off of theprinting apparatus.

The program ROM 1035 stores programs for an image information generator1037, color/monochrome mode setting unit 1060, printing execution unit1061, print mode decision unit 1062, and discharge completion monitoringunit 1063. The image information generator 1037 generates various imageobjects in accordance with settings of data received from the hostcomputer 1001. The color/monochrome mode setting unit 1060 designatesswitching of color/monochrome printing in accordance with colorinformation and print settings of the pages of color and monochromedocuments sent from the host computer 1001. The printing execution unit1061 executes processing of sending a generated printable image objectto an engine unit. The print mode decision unit 1062 decides inaccordance with the situation whether to instruct the engine of a coloror monochrome print mode for a page to be printed. The dischargecompletion monitoring unit 1063 monitors whether a sheet bearing aprinted page has been discharged without any error such as jam.

Reference numeral 1038 denotes a bitmap image mapping/transfer unitwhich maps data into a bitmap image and transfers the mapped bitmapimage to a printing apparatus engine unit 1039; 1040, an engine I/Fwhich connects the controller 1031 and the printing apparatus engineunit 1039 for actually printing on a sheet; 1042, a panel I/F whichconnects the controller 1031 and an operation panel 1041; 1044, a memoryI/F which connects an external memory 1043 and the controller 1031; and1045, a system bus which connects units within the above-mentionedcontroller 1031.

The operation panel 1041 allows operating the printing apparatus. Theexternal memory 1043 is used to save print data and various pieces ofinformation about the printing apparatus.

The printing apparatus engine unit (to be referred to as an engine unithereinafter) 1039 actually prints on a print sheet. The engine unit 1039comprises an engine controller 1046 which controls printing from sheetfeed to data printing and discharge, and a color/monochrome printingcontroller 1047 which switches between a color print mode in which colorprint processing is performed using Y (Yellow), M (Magenta), C (Cyan),and K (blacK), and a monochrome print mode in which monochrome printprocessing is performed using only K.

Results of determining from data contents whether to print a generatedimage in color or monochrome upon image information generation will becalled color and monochrome modes. In the fifth embodiment, the colormode targets a page containing a color image object (i.e., color page),and the monochrome mode targets a page containing no color image object(i.e., monochrome page). A mode in which color printing operation isactually performed by the engine controller 1046 using Y, M, C, and Kmechanisms will be called a color print mode. A mode in which monochromeprinting operation is done using only K will be called a monochromeprint mode.

FIG. 11 is a sectional view showing the arrangement of the engine unit1039 of the color laser beam printer 1030. As shown in FIG. 11, thecolor laser beam printer 1030 comprises a housing 3001. The housing 3001incorporates mechanisms for constituting the engine unit 1039, and acontrol board storage unit 3003 which stores the engine controller 1046and printer controller 1031 (shown in FIG. 10) for controlling eachprint process processing by each mechanism.

The color laser beam printer 1030 comprises four photosensitive drums3010 (3010K, 3010M, 3010C, and 3010Y) serving as image carriers whichare arranged vertically. The photosensitive drums 3010 are rotated anddriven counterclockwise in FIG. 10 by a driving means (not shown). Thephotosensitive drums 3010 are surrounded in the rotational direction bycharging devices 3011 (3011K, 3011M, 3011C, and 3011Y) which uniformlycharge the surfaces of the photosensitive drums 3010, scanners 3012(3012K, 3012M, 3012C, and 3012Y) which emit laser beams on the basis ofimage information to form electrostatic latent images on thephotosensitive drums 3010, developing devices 3013 (3013K, 3013M, 3013C,and 3013Y) which apply toner to electrostatic latent images to developthe images as toner images, an electrostatic convey/transfer device 3014which transfers toner images on the photosensitive drums 3010 onto atransfer medium, and cleaning devices 3015 (3015K, 3015M, 3015C, and3015Y) which remove toner left on the surfaces of the photosensitivedrums 3010 after transfer. Note that the photosensitive drums 3010,charging devices 3011, developing devices 3013, and cleaning devices3015 are integrated into cartridges, forming drum-integrated processcartridges 3016 (3016K, 3016M, 3016C, and 3016Y). These processcartridges 3016 are detachable from the housing 3001.

The arrangements of the respective units will be sequentially explained.Each photosensitive drum 3010 is constituted using an organicphotoconductive layer (OPC photosensitive member). The photosensitivedrum 3010 is freely rotatably supported by support members at two ends.A driving force from a driving motor (not shown) is transmitted to oneend, rotating and driving the photosensitive drum 3010 counterclockwisein FIG. 11.

Each charging device 3011 is a conductive roller formed into a rollershape. This roller is brought into contact with the surface of thephotosensitive drum 3010. A charging bias voltage is applied from apower supply (not shown) to the roller, uniformly charging the surfaceof the photosensitive drum 3010.

The scanners 3012 are horizontally arranged beside the photosensitivedrums 3010. Image beams corresponding to image signals from laser diodes(not shown) irradiate polygon mirrors 3028 (3028K, 3028M, 3028C, and3028Y) rotated at a high speed by a scanner motor. The image beamsreflected by the polygon mirrors selectively illuminate the surfaces ofthe charged photosensitive drums 3010 via imaging lenses 3017 (3017K,3017M, 3017C, and 3017Y), forming electrostatic latent images.

The developing devices 3013 (3013K, 3013M, 3013C, and 3013Y) are formedfrom developing units which respectively contain yellow, cyan, magenta,and black toners sequentially from the upstream of the transfer mediumconvey direction (lower portion in FIG. 11). In developing electrostaticlatent images on the photosensitive drums 3010, toners in the containersof the corresponding developing units are supplied to spreading rollers3013 k 1, 3013 m 1, 3013 c 1, and 3013 y 1 by supply mechanisms. Thetoners are applied as thin layers to the outer surfaces of rotatingdeveloping rollers 3013 k 2, 3013 m 2, 3013 c 2, and 3013 y 2. At thesame time, the toners are charged (triboelectrification). By applying adeveloping bias between the developing rollers and the photosensitivedrums 3010 bearing the electrostatic latent images, the toners aredeposited onto the electrostatic latent images to develop the images astoner images.

Each cleaning device 3015 removes so-called residual toner which is nottransferred and remains on the surface of the photosensitive drum 3010after toner deposited on the photosensitive drum 3010 by the developingdevice 3013 is transferred onto a transfer medium.

An electrostatic convey belt 3008 serving as a belt member is sodisposed as to face all the photosensitive drums 3010K, 3010M, 3010C,and 3010Y and circulate in contact with them. The electrostatic conveybelt 3008 is vertically supported by rollers with four shafts. Theelectrostatic convey belt 3008 circulates such that a transfer medium iselectrostatically chucked by the outer surface on the left side in FIG.11, and brought into contact with the photosensitive drums 3010. Anattraction roller 3009 is in contact with the electrostatic convey belt3008 on the upstream of the transfer medium convey direction (lowerportion in FIG. 11). In conveying a transfer medium, a bias voltage isapplied to the attraction roller 3009 to form an electric field betweenthe attraction roller 3009 and a grounded roller 3018 a. Dielectricpolarization is generated between the electrostatic convey belt 3008 andthe transfer medium to generate an electrostatic chuck force betweenthem.

Accordingly, the transfer medium is conveyed to transfer positions bythe electrostatic convey belt 3008, and toner images on thephotosensitive drums 3010 are sequentially transferred. Transfer rollers3019 (3019K, 3019M, 3019C, and 3039Y) are arranged as transfer membersin contact with the inner surface (back surface) of the electrostaticconvey belt 3008 in correspondence with the four photosensitive drums3010K, 3010M, 3010C, and 3010Y. The transfer rollers 3019 are connectedto a transfer bias power supply (not shown). The transfer rollers 3019face the corresponding photosensitive drums 3010, and form transferportions. Positive charges are applied from the transfer rollers 3019 tothe transfer medium via the electrostatic convey belt 3008. Electricfields by the charges transfer negatively charged toner images on thephotosensitive drum 3010 to the transfer medium in contact with thephotosensitive drum 3010.

The electrostatic convey belt 3008 is looped by four rollers: a drivingroller 3020, driven rollers 3018 a and 3018 b, and tension roller 3021.The electrostatic convey belt 3008 rotates clockwise in FIG. 11. Whilethe electrostatic convey belt 3008 circulates to transfer a transfermedium from the driven roller 3018 a to the driving roller 3020, tonerimages on the photosensitive drums are transferred.

A feed unit 3022 feeds a transfer medium to an image forming portion,and a plurality of transfer media 3004 are stored in a feed cassette3005. In image formation, a pickup roller (semilunar roller) 3006 and apair of registration rollers 3007 are driven and rotated in accordancewith image formation operation, and separately feed transfer media inthe feed cassette 3005 one by one. The leading end of each transfermedium runs into the pair of registration rollers 3007, temporarilystops, forms a loop, and then is fed again to the electrostatic conveybelt 3008.

A fixing unit 3023 fixes a plurality of toner images transferred to atransfer medium. The fixing unit 3023 is made up of a heating roller3024 which is driven and rotated, and a press roller 3025 which is inpress contact with the heating roller 3024 and applies heat and pressureto a transfer medium.

More specifically, a transfer medium to which toner images on thephotosensitive drums 3010 are transferred is conveyed by a pair offixing rollers when passing through the fixing unit 3023, and receivesheat and pressure from the pair of fixing rollers 3024 and 3025. As aresult, toner images in a plurality of colors are fixed onto the surfaceof the transfer medium.

The yellow, magenta, and cyan process cartridges 3016Y, 3016M, and 3016Care constituted such that the photosensitive drums 3010Y, 3010M, and3010C move left by an elevating mechanism (not shown) from states incontact with the electrostatic convey belt 3008 to positions spacedapart from the electrostatic convey belt 3008. The elevating mechanismoperates in accordance with a selected print mode. That is, when thecolor print mode is designated by the color/monochrome printingcontroller 1047 in the engine controller 1046, the photosensitive drums3010Y, 3010M, and 3010C come into contact with the electrostatic conveybelt 3008. Toner images on the photosensitive drums 3010 are transferredsequentially from yellow, magenta, cyan, and black by voltageapplication from the transfer rollers 3019Y, 3019M, 3019C, and 3019K.

When the monochrome print mode is designated, the elevating mechanismmoves the photosensitive drums 3010Y, 3010M, and 3010C apart from theelectrostatic convey belt 3008. Only the photosensitive drum 3010K is incontact with the electrostatic convey belt 3008, and a toner image onthe photosensitive drum 3010K is transferred in only black by voltageapplication from the transfer roller 3019K. In the color print mode, acolor document is not always printed. A monochrome document can beprinted in the color print mode by the same operation except that atoner image is formed in only black. In the monochrome print mode, atransfer medium may pass through C, M, and Y drum positions at a highspeed, realizing high-speed processing.

In this manner, the transfer medium 3004 bearing a toner image isseparated from the electrostatic convey belt 3008 by the driving roller3020, and reaches the fixing unit 3023. The toner image is thermallyfixed onto the transfer medium 3004, and the transfer medium 3004 isdischarged to a discharge portion FD by a pair of discharge rollers3026.

An operation panel 3002 which constitutes the operation panel 1041 isattached to the housing 3001. The operation panel 3002 has switches forinputting instructions, an LED display for displaying information, andan LCD display. The operation panel 3002 also has an external memory3027 for implementing the external memory 1043 used by the printercontroller to store print data or the like.

As described above, the color laser beam printer 1030 operates even inthe monochrome print mode. In this case, the yellow, cyan, and magentaphotosensitive drums are spaced apart from the electrostatic conveybelt. This reduces contact with the convey belt, prolonging the servicelives of the yellow, cyan, and magenta photosensitive drums. Inaddition, the toner consumption amount can be suppressed. However,rotating the motor wears a contact portion. When monochrome printing isdone in the color print mode, the operation is the same as that in thecolor print mode, and the yellow, cyan, and magenta photosensitive drumsrotate (idle rotation) without any printing. For this reason, theyellow, cyan, and magenta photosensitive drums wear along with idlerotation owing to friction between the developing device and the contactportion, wasteful toner removal, and the like.

The operation of the printer controller having the above-describedsystem configuration will be explained.

If the user instructs the host computer 1001 to execute printing, acontrol code and data are sent via the network 1002 and communicationline 1003 to a printing apparatus (in this case, the color laser beamprinter 1030) designated by the instruction. The printer 1030 receivesdata sent from the I/O unit 1032, temporarily stores it in the I/Obuffer 1033, and then accumulates the received data in the RAM 1036.

The CPU 1034 processes the received data in accordance with a programdescribed in the program ROM 1035. That is, the image informationgenerator 1037 processes data, generating image information on each(image object) of graphic, character, and image data. After pieces ofimage information on all image objects in one page to be printed aregenerated, the color/monochrome mode setting unit 1060 sets either acolor mode or monochrome mode for the page on the basis of designationof the color mode from the host computer and determination of whether acolor image object exists. At the end of generation for one page, piecesof image information are transferred to processing of the printingexecution unit 1061.

The printing execution unit 1061 monitors a page generated by the imageinformation generator 1037 and color/monochrome mode setting unit 1060,and checks whether the page can be printed. If so, the print modedecision unit 1062 is activated to decide, on the basis of settingcontents by the color/monochrome mode setting unit 1060 and the printingstate of the printer 1030, whether to actually operate the engine unit1039 in the color or monochrome print mode. The decision content of theprint mode decision unit 1062 is set in the color/monochrome printingcontroller 1047 within the engine controller 1046 via the engine I/F1040.

Image information to be printed is supplied from the printing executionunit 1061 to the bitmap image mapping/transfer unit 1038 where the imageinformation is mapped into a bitmap image. The bitmap image is sent tothe printing apparatus engine unit 1039 via the engine I/F 1040. Theprinting apparatus engine unit 1039 prints the supplied bitmap image ona transfer medium in the designated print mode. The transfer medium isdischarged from a designated discharge port.

Processing in the image information generator 1037, color/monochromemode setting unit 1060, printing execution unit 1061, and print modedecision unit 1062 will be explained in more detail.

FIG. 12 shows a processing flow in the image information generator 1037and color/monochrome mode setting unit 1060. After data is received andthe image information generator 1037 starts generating imageinformation, whether pieces of image information of all pages have beengenerated is checked (step S2001). If pieces of image information of allpages have not been generated (NO in step S2001), pieces of settinginformation of each page such as the color mode, resolution, tone level,sheet size, and feed stage of a page designated from the panel or hostcomputer are saved as attributes of a page to be generated (step S2002).Whether the page has been generated is then checked (step S2003). If thepage has not been generated (NO in step S2003), data sent by PDL (PageDescription Language) or the like is analyzed (step S2004), and an imageobject in the intermediate data format that designates a print positionand shape is generated (step S2005).

Color/monochrome mode designation for data sent from the host computer1001 is checked (step S2006). If the data designation does not representthe monochrome mode (NO in step S2006), whether the generated objectcontains color data is checked (step S2007). If the data designationrepresents the monochrome mode (YES in step S2006), the flow returns tostep S2003. Processing from step S2004 to step S2007 is repeated tillthe end of page generation processing.

If the page has been generated (YES in step S2003), whether the pagecontains a color object is checked (step S2008). That is, the presenceof an object determined in step S2007 to be a color object is checked.

If no object is determined in step S2007 to be a color object, or if themonochrome mode not subjected to the check in step S2007 is designated,the flow shifts from step S2008 to step S2010, and page information isset in the monochrome mode. To transfer control to the printingexecution unit 1061, the page is registered in the page queue (stepS2011). If a color object is determined in step S2008 to exist, the flowshifts to step S2009. In this case, since printing must be done in thecolor print mode, the printing apparatus engine unit 1039 is set in thecolor mode (step S2009), and the page is registered in the page queue(step S2011).

The above processing is repeated until all pieces of image informationare generated (NO in step S2001). After processing shown in FIG. 12ends, the color mode/monochrome mode representing whether to print incolor or monochrome is set. Note that this mode setting is determinedfrom image information.

Processing in the printing execution unit 1061 will be explained withreference to the flow chart of FIG. 13.

Whether a page whose image information has been generated exists ischecked by referring to the page queue (step S4001). If no page existsin the page queue (NO in step S4001), the check in step S4001 isrepeated until a page is generated. If a page exists in the page queue(YES in step S4001), a page to be printed next is selected from the pagequeue (step S4002), and the flow shifts to print mode decision/settingprocessing (step S4003). Processing in step S4003 is processing by theprint mode decision unit 1062.

Processing in the print mode decision unit 1062 will be described withreference to the flow chart of FIG. 14. The fifth embodiment adopts analgorithm of deciding a color or monochrome print mode by referring toinformation of one succeeding page which waits for the start of printingupon the completion of generating image information.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is referred to (step S5001). For the color mode(YES in step S5002), the page can only be printed in the color printmode. The color print mode is set in the engine unit 1039 via the engineI/F 1040 (step S5003), and print mode decision/setting processing ends.

For the monochrome mode (NO in step S5002), whether image information ofa page next to the selected page has been generated is checked byreferring to the page queue (step S5004). If no next page exists in thepage queue (NO in step S5004), the monochrome print mode is set in theengine unit 1039 via the engine I/F 1040 (step S5005), and print modedecision/setting processing ends.

If the next page exists in the page queue (YES in step S5004), which ofthe color and monochrome modes has been set for the next page by thecolor/monochrome mode setting unit 1060 in image information generationis checked (step S5006). If the color mode has been set (YES in stepS5007), the color print mode is set in the engine unit 1039 (stepS5008), and print mode decision/setting processing ends. If themonochrome mode has been set (NO in step S5007), the monochrome printmode is set in the engine unit 1039 (step S5005), and print modedecision/setting processing ends.

Referring back to processing in FIG. 13, various settings such as feedstage setting are performed in the engine unit 1039 (step S4004). If thecolor print mode is designated to perform printing in step S4003 (NO instep S4005), color images are mapped at Y, C, M, and K timings andtransferred to the engine unit 1039 (steps S4006, S4007, S4008, andS4009). At this time, if an immediately preceding page is printed in themonochrome print mode, the print mode is switched to the color printmode (step S4005 a).

If image information is monochrome, no Y, C, or M object exists, and noimage is mapped/transferred at the Y, C, or M timing. Hence, if themonochrome print mode is designated to perform printing (YES in stepS4005), only a monochrome image is mapped at the K timing andtransferred to the engine unit 1039 (step S4009). At this time, if animmediately preceding page is printed in the color print mode, the printmode is switched to the monochrome print mode (step S4005 b).

In order to monitor whether discharge is completed without any error,the page is registered in a discharge queue (step S4010). The flow thenreturns to processing starting from step S4001 in order to process thenext page.

Although not shown, a predetermined time is required from steps S4006 toS4009 due to a timing at which an image is transferred to the engine.This results in a time interval before the timing in step S4003 for eachpage. The next page accumulated in the page queue is checked at thesetting timing in step S4003.

A setting example of the print mode according to the fifth embodimentdescribed above will be explained with reference to FIG. 15. In FIG. 15,each rectangle represents one page, and a mode decided by thecolor/monochrome mode setting unit 1060 upon generating each imageinformation is described in each rectangle. At the start of printingPage 1, pieces of image information up to Page 6 have been generated andregistered in the page queue, as shown in FIG. 15. In this case, theprint mode decision unit 1062 designates the color print mode for Page 1because the color mode is designated for the next page Page 2. As aresult, respective pages are printed in print modes designated belowpage frames in FIG. 16. Upon the completion of discharge, pages aredeleted from the discharge queue in accordance with an end notificationfor each page from the engine unit 1039. Print mode switching processingoccurs between Page 4 and Page 5 in accordance with the above-describedprocessing, as shown in FIG. 16.

If an error occurs, continuous driving of the scanner motor ormaintenance of the fixing unit at a high temperature degrades componentsin a printing apparatus such as a laser printer. To prevent this, aspecific time for continuous printing exists, and when, e.g., settingoperation for the next page exceeds the specific time, the engine unit1039 temporarily stops. This situation is, e.g., generation of an errorsuch as jam or toner shortage. If image information generation takes along time, page creation may delay, failing to execute printing before acontinuous printing timing. Also in this case, the engine unit 1039stops.

To cope with the stop of the engine unit, the printing apparatusaccording to the fifth embodiment monitors the completion of discharge,detects a page which has been output before the stop of the engine and apage which has not been output yet, and performs again processing fromprint mode setting for a page which has not been output yet. Processingin the discharge completion monitoring unit 1063 will be explained withreference to the flow chart of FIG. 21.

After discharge completion monitoring starts at the same time aspower-on, the error state of the printer is checked (step S12001). If noerror occurs (NO in step S12001), processing in step S12001 is repeatedto monitor an error. Upon generation of an error such as the absence ofany sheet on a selected feed stage, jam, toner shortage, the end of theservice life of the drum, or a failure in discharge due to a dischargeport full of sheets (YES in step S12001), whether pages remain in thedischarge queue is checked (step S12002). Note that the case for YES instep S12001 includes not only generation of an error but also a casewherein page creation processing exceeds a specific time.

If pages remain in the discharge queue (YES in step S12002), pagesregistered in the discharge queue are read out and selected from a newone (step S12003), and set again in the page queue (step S12004). Theflow returns to step S12002 to perform processing of returning all pagesleft in the discharge queue to the page queue. If no page remains in thedischarge queue (NO in step S12002), print processing restarts (stepS12005), and the flow returns to processing in step S12001 again. Inthis case, print processing interrupts during the course of step S4001to S4010, and the engine unit 1039 temporarily stops. Thus, printprocessing restarts, a page left in the page queue is processed again,processing from step S4001 is executed, and print mode setting in stepS4003 is also done again.

As described above, according to the fifth embodiment, frequentswitching between the color and monochrome print modes can be prevented,and high throughput can be maintained by referring to image informationof a succeeding page and determining a print mode. When the same printmode continues, a proper print mode is decided to perform printing,which can minimize degradation of each engine component.

If the engine unit 1039 temporarily stops due to an error, the printmode is set again. This can prevent unwanted print mode switching inpage setting owing to printing in a previously set print mode when theengine unit temporarily stops in a state in which a page assigned themonochrome mode is set in the color print mode.

Sixth Embodiment

In the fifth embodiment, a page accumulated in the page queue isreferred to regardless of the timing in order to decide the color printmode. It is also possible to calculate print mode decision limit time(limit time within which the print mode switching start timing does notinfluence the throughput) for switching between the color and monochromeprint modes within the shortest time during continuous printing, and todecide a print mode after waiting for accumulation of a page in the pagequeue by the time.

The arrangement of a color laser beam printer and the operation of aprinter controller according to the sixth embodiment are almost the sameas those in the fifth embodiment except print mode decision/settingprocessing (step S4003) in FIG. 13.

The processing flow of a print mode decision unit 1062 according to thesixth embodiment will be described with reference to FIG. 17. The sixthembodiment also adopts an algorithm of deciding a color or monochromeprint mode by referring to information of one succeeding page whichwaits for the start of printing upon the completion of generating imageinformation.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is referred to (step S8001). For the color mode(YES in step S8002), the page can only be printed in the color printmode. The color print mode is set in an engine unit 1039 (step S8003),and print mode decision/setting processing ends.

For the monochrome mode (NO in step S8002), in order to calculate aprint mode settable time, various pieces of information of the engineunit 1039 such as the feed timing of a sheet for a preceding page andthe current operation state are acquired. A print mode settable limittime is calculated from the acquired information (step S8004). The flowwaits till the limit time (step S8005). Whether image information of apage next to the selected page has been generated is checked byreferring to the page queue (step S8006). In FIG. 17, the print modesettable limit time is calculated every time a page in the monochromemode is detected. It is also possible to calculate the limit time onlyonce and use the calculation result in subsequent processing.Alternatively, the limit time may be calculated depending on the timewhen the flow reaches processing in step S8004 or every time engineoperation changes in accordance with the sheet size or the like.

If no next page exists (NO in step S8006), the monochrome print mode isset in the engine unit 1039 (step S8007), and print modedecision/setting processing ends. If the next page exists in the pagequeue (YES in step S8006), which of the color and monochrome modes hasbeen set for the next page by a color/monochrome mode setting unit 1060is checked (step S8008). If the color mode has been set (YES in stepS8009), the color print mode is set in the engine unit 1039 (stepS8010), and print mode decision/setting processing ends. If themonochrome mode has been set (NO in step S8009), the monochrome printmode is set in the engine unit 1039 (step S8007), and print modedecision/setting processing ends.

Referring back to processing in FIG. 13, the same processing as that inthe fifth embodiment is performed. Switching from the color print modeto the monochrome print mode occurs only when switching is determinednecessary. For designation before the print mode setting limit time,operation necessary for switching can be achieved within the shortesttime. Image information of a subsequent page can be generated during thewait time. The sixth embodiment can cope with even data which takes along time for processing a subsequent page.

As described above, according to the sixth embodiment, decision of thecolor mode waits till the print mode switching limit time for the imageobject of a succeeding page in which the print mode can be switched. Thethroughput can be more reliably maintained, and accurate print modeswitching can be realized even if image information generationprocessing for a succeeding page takes a long time.

Seventh Embodiment

In the fifth embodiment, the color print mode is decided by referring tothe color/monochrome mode of a succeeding page. The print mode can alsobe decided by referring to the print mode of a previously printed pageand/or the color/monochrome mode. In the seventh embodiment, this printmode decision method will be described.

Also in the seventh embodiment, the arrangement of a color laser beamprinter and the operation of a printer controller are almost the same asthose in the fifth embodiment except print mode decision/settingprocessing in FIG. 13.

FIG. 18 shows the processing flow of a print mode decision unitaccording to the seventh embodiment. The seventh embodiment employs analgorithm of calculating the ratio of the monochrome print mode of apage by referring to pieces of information of three preceding pageswhich have been printed or are being printed upon the completion ofsetting a print mode, and deciding a color or monochrome print mode byusing the calculation result. In the following description, the printmode of a page is decided by referring to the print mode of a precedingpage whose print process has been determined. Alternatively, acolor/monochrome mode determined for a preceding page may be referredto, or a combination of a print mode and color/monochrome mode may bereferred to.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is referred to (step S9001). For the color mode(YES in step S9002), the page can only be printed in the color printmode. The color print mode is set in an engine unit 1039 (step S9003),and print mode decision/setting processing ends.

For the monochrome mode (NO in step S9002), whether a page which hasbeen printed or is being printed upon the completion of setting a printmode exists is checked (step S9004). If no such page exists (NO in stepS9004), the monochrome print mode set in image information generation isset in the engine unit 1039 (step S9005), and print modedecision/setting processing ends.

If a page which has been printed exists in step S9004 (YES in stepS9004), the ratio of the monochrome print mode is calculated byreferring to the print modes of three pages (step S9006). If the ratioof the monochrome print mode is lower than, e.g., 30% (NO in stepS9007), the color print mode is set in the engine unit 1039 (stepS9008), and print mode decision/setting processing ends. If the ratio isequal to or higher than 30% (YES in step S9007), the monochrome printmode is set in the engine unit 1039 (step S9005), and print modedecision/setting processing ends.

Referring back to processing in FIG. 13, the same processing as that inthe fifth embodiment is performed.

Assume that the print modes of up to Page 4 have been set and thesepages have been printed-when deciding the print mode of Page 5 in FIG.19. In FIG. 19, each rectangle represents one page, and a mode decidedupon generating each image information is described within each frame.An actually decided print mode is described outside the frame.

Monochrome printing occupies ⅓ by referring to the print modes of threepreceding pages Page 2, Page 3, and Page 4. The ratio is 30% or more,and the monochrome print mode is designated for Page 5. A print modedescribed below each page frame is designated for each page, and thenthe page is printed.

As described above, according to the seventh embodiment, the actualoperation status of the engine unit 1039 can be obtained by referring toprinted pages. A mode for use can be predicted from the use status ofthe printing apparatus, and frequency switching can be prevented suchthat a print mode used many times is set as much as possible.

The use of the ratio of the monochrome and color print modes can realizefine setting such that the switching criterion quantitatively takesnumerical form and switching is so set as to be performed at a properratio in consideration of the degree of wear and the influence ofswitching in terms of the characteristics of the engine unit 1039 bypretest before shipping a product.

The seventh embodiment uses information on the print modes of threepreceding pages. Alternatively, information after cartridge exchange orthe first power-on operation may be held and exploited.

In the seventh embodiment, the print mode is referred to. Alternatively,the print mode of a target page may be decided by referring to the ratioof the color and monochrome modes of preceding pages. The print mode ofa target page may be decided by referring to a combination of the ratioof the print modes of preceding pages and the ratio of the color andmonochrome modes.

In the seventh embodiment, the ratio of the print mode is applied to aprinted page. Also, a future printing status can be predicted byapplying the ratio of the print mode to the color/monochrome mode of apage accumulated in the page queue.

As described above, according to the seventh embodiment, an actualengine operation state can be obtained by referring to a printed page. Amode for use can be predicted from the use status of the printingapparatus, and frequent switching can be prevented such that a printmode used many times is set as much as possible.

The use of the ratio of the monochrome and color print modes can realizefine setting such that the switching criterion quantitatively takesnumerical form and its value is calculated from engine characteristicsand the like.

Eighth Embodiment

In the fifth embodiment, the print mode of a current page is decided byreferring to the color/monochrome mode of a succeeding page. The printmode of a succeeding page may be decided at the same time as the printmode of the current page. In the eighth embodiment, this method will bedescribed.

Also in the eighth embodiment, the arrangement of a color laser beamprinter and the operation of a printer controller are almost the same asthose in the fifth embodiment except print mode decision/settingprocessing in FIG. 13.

FIG. 22 shows the processing flow of a print mode decision unitaccording to the eighth embodiment. Similar to the fifth embodiment, theeighth embodiment employs an algorithm of deciding a color or monochromeprint mode by referring to information of one succeeding page whichwaits for the start of printing upon the completion of generating imageinformation. An algorithm of deciding a print mode in advance inaccordance with the situation is also applied to the referred page.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is referred to (step S13001). If the color modehas been set (YES in step S13002), the page can only be printed in thecolor print mode. The color print mode is set in an engine unit 1039(step S13003), and print mode decision/setting processing ends.

For the monochrome mode (NO in step S13002), whether the print mode ofthe selected page has been decided is checked (step S13004). If theprint mode has been decided (YES in step S13004), the set print mode isset in the engine unit 1039 (step S13010). If the print mode of theselected page has not been decided (NO in step S13004), whether imageinformation of a page next to the selected page has been generated ischecked by referring to the page queue (step S13005).

If image information of the next page has not been generated (NO in stepS13005), the monochrome print mode set in image information generationis directly set in the engine unit 1039 (step S13006), and print modedecision/setting processing ends. If image information of the next pageexists (YES in step S13005), which of the color and monochrome modes hasbeen set for the next page is checked (step S13007). If the color modehas been set for the next page (YES in step S13008), the color printmode is set in the engine unit 1039 (step S13003), and print modedecision/setting processing ends. If the monochrome mode has been set(NO in step S13008), the monochrome print mode is decided as the printmode of the next page, and also set as the print mode of the currentpage in the engine unit 1039 (step S13009). Print mode decision/settingprocessing then ends.

Similar to the fifth embodiment, assume that the pieces of imageinformation of up to Page 6 have been generated in the page queue inprinting Page 1, as shown in FIG. 15. Since the color mode is designatedfor the next page Page 2, the color print mode is also designated forPage 1. When the monochrome print mode is decided for Page 4, themonochrome print mode is also decided as the print mode of the next pagePage 5. Hence, the print mode of each page is decided as shown beloweach page frame in FIG. 23, and the page is printed.

As described above, the next print mode is permanently decided from apredetermined combination of the print mode setting of a current pageand the color/monochrome mode of a succeeding page. Finer print modedesignation according to the combination can be achieved.

Ninth Embodiment

In the fifth embodiment, the color print mode is decided by referring tothe color/monochrome mode of a succeeding page. The print mode can alsobe decided by referring to the print mode of a previously printed pagewhen image information of a succeeding page is not generated. The ninthembodiment adopts this method.

Also in the ninth embodiment, the arrangement of a color laser beamprinter and the operation of a printer controller are almost the same asthose in the fifth embodiment except print mode decision/settingprocessing in FIG. 13.

FIG. 24 shows the processing flow of a print mode decision unitaccording to the ninth embodiment. Similar to the fifth embodiment, theninth embodiment adopts an algorithm of deciding a color or monochromeprint mode by referring to information of one succeeding page whichwaits for the start of printing upon the completion of generating imageinformation. Further, an algorithm of deciding a print mode by referringto the print mode of a previously printed page is applied to a casewherein image information of a succeeding page has not been generated.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is referred to (step S15001). If the color modehas been set (YES in step S15002), the page can only be printed in thecolor print mode. The color print mode is set in an engine unit 1039(step S15003), and print mode decision/setting processing ends.

For the monochrome mode (NO in step S15002), whether image informationof a page next to the selected page has been generated is checked byreferring to the page queue (step S15004). If image information of thenext page exists (YES in step S15004), which of the color and monochromemodes has been set for the next page is checked (step S15005). For thecolor mode (YES in step S15006), the color print mode is set in theengine unit 1039 (step S15007), and print mode decision/settingprocessing ends. For the monochrome mode, the monochrome print mode setin image information generation is set in the engine unit 1039 (stepS15010), and print mode decision/setting processing ends.

If no next page exists (NO in step S15004), the setting of the printmode ends, and whether a page which has been printed or is being printedexists is checked (step S15008). If no such page exists (NO in stepS15008), the monochrome print mode set in image information generationis set in the engine unit 1039 (step S15010), and print modedecision/setting processing ends. If such a page exists (YES in stepS15008), whether the print mode of one preceding page is the color printmode is checked (step S15009). For the color print mode (YES in stepS15009), the color print mode is set in the engine unit 1039 (stepS15003), and print mode decision/setting processing ends. For themonochrome print mode (NO in step S15009), the monochrome print mode isset in the engine unit 1039 (step S15010), and print modedecision/setting processing ends.

According to the ninth embodiment, when image information of asucceeding page is not generated, information of the succeeding page andinformation of a previously printed page are combined by referring tothe print mode of the previously printed page. Even if the final page ismonochrome, it can be printed without switching the print mode. Printingcan be done without decreasing the throughput.

10th Embodiment

In the ninth embodiment, the color print mode is decided by referring tothe color/monochrome mode of a succeeding page. Further, the print modeis decided in accordance with the situation by simultaneously referringto the print mode of a printed page. It is also possible to set a printmode switching pattern in advance and designate a print mode inaccordance with the pattern. In the 10th embodiment, this method will bedescribed.

The arrangement of a color laser beam printer and the operation of aprinter controller according to the 10th embodiment are almost the sameas those in the ninth embodiment except print mode decision/settingprocessing in FIG. 24.

FIG. 25 shows the processing flow of a print mode decision unitaccording to the 10th embodiment. In addition to the algorithm of theninth embodiment, the 10th embodiment adopts an algorithm of setting apattern in advance and deciding a print mode in accordance with theprint mode setting pattern in the presence of a previously printed pageand a succeeding page which waits for the start of printing upon thecompletion of generating image information.

After print mode decision/setting processing starts, which of the colorand monochrome modes has been set for a selected page in imageinformation generation is checked (step S16001). For the color mode (YESin step S16002), the page can only be printed in the color print mode.The color print mode is set in an engine unit 1039 (step S16003), andprint mode decision/setting processing ends.

For the monochrome mode (NO in step S16002), whether image informationof a page next to the selected page has been generated is checked byreferring to the page queue (step S16004). If image information of thenext page does not exist (NO in step S16004), whether a page which hasbeen printed or is being printed upon the completion of setting a printmode exists is checked (step S16005). If no such page exists (NO in stepS16005), the monochrome print mode set in image information generationis set in the engine unit 1039 (step S16007), and print modedecision/setting processing ends.

If a page which precedes the target page and completes print modesetting exists (YES in step S16005), whether the print mode used toprint one preceding page is the color print mode is checked (stepS16006). For the color print mode (YES in step S16006), the color printmode is set in the engine unit 1039 (step S16003), and print modedecision/setting processing ends. For the monochrome mode (NO in stepS16006), the monochrome print mode is set in the engine unit 1039 (stepS16007), and print mode decision/setting processing ends.

In step S16004, whether image information of the next page has beengenerated is checked by referring to the page queue. If imageinformation is determined to have been generated (YES in step S16004),whether a page which has been printed or is being printed upon thecompletion of setting a print mode exists is checked (step S16008). Ifno such page exists (NO in step S16008), which of the color andmonochrome modes has been set for the next page is checked (stepS16010). If the color mode has been set (YES in step S16010), the colorprint mode is set in the engine unit 1039 (step S16011), and print modedecision/setting processing ends. If the color mode has not been set (NOin step S16010), the monochrome print mode is set in the engine unit1039 (step S16007), and print mode decision/setting processing ends.

If the printed page exists in step S16008, designation of acolor/monochrome mode for one subsequent page, the print mode of onepreceding printed page, and a color/monochrome mode determined fororiginal image information as shown in FIG. 26 are referred to. Patternsare searched for the same pattern (step S16012), the print mode is setin the engine unit 1039 in accordance with the result (right designationin FIG. 26), and print mode decision/setting processing ends.

According to the 10th embodiment, an assumed print mode switchingpattern is set in advance, and the print mode is designated inaccordance with the pattern. The degree of wear and the influence ofswitching are examined in accordance with the switching pattern in termsof the characteristics of the engine unit 1039 before shipping aproduct. Settings are embedded every pattern so as to appropriatelyswitch the print mode, realizing finer setting.

The control according to the fifth to 10th embodiments enables settingwhich puts importance on the throughput, setting which suppresses thewear of expendables, and flexible setting which balances them, achievingfiner print mode designation. For example, by referring to the pastprint mode in the seventh embodiment, print mode setting can bedynamically changed. In the eighth embodiment, the print mode of asucceeding page can also be decided at the same time as that of thecurrent page. The 10th embodiment can cope with various combinations bypatterning combinations of print modes, and color and monochrome modes.Further, finer flexible print mode designation can be performed bypattern matching during printing with a combination.

The system may be so constituted as to allow the user to performsetting/registration of the ratio value and the number of past pages tobe referred to in the seventh embodiment, setting/registration of acombination pattern used to decide the print mode of the next pattern inthe ninth embodiment, and setting/registration of a switching pattern orthe like in the 10th embodiment.

It is apparent that discharge completion monitoring processing describedin the fifth embodiment with reference to FIG. 21 can be applied to eachof the sixth to 10th embodiments. Unwanted switching can beadvantageously suppressed by preventing continuous use of a print modeset for a page during printing even upon engine-off.

As described above, the present invention realizes print mode switchingprocessing which satisfies both the service life of a unit and thethroughput of print processing.

11th Embodiment

FIG. 27 is a block diagram showing the schematic configuration of animage printing system to which a printer according to the 11thembodiment of the present invention can be applied.

In FIG. 27, a data processing device 5101 is constituted by, e.g., acomputer, and functions as an image information supply source or printercontrol device. In the 11th embodiment, a laser beam printer (printer)is used as a printer 5102. The printer applied in the 11th embodiment isnot limited to the laser beam printer, and may be another printing typeprinter such as an inkjet printer.

A video controller 5103 generates raster data for each page on the basisof image information (e.g., ESC code or page description language)supplied from the data processing device 5101. The video controller 5103sends the raster data to a printer engine 5105.

The printer engine 5105 forms a latent image on a photosensitive drum onthe basis of the raster data supplied from the video controller 5103.The latent image is transferred and fixed (electrophotography) on aprint medium, thereby printing the image.

A panel 5104 is used as a user interface. The user operates the panel5104 to designate a desired operation. The panel 5104 displays theprocessing contents of the printer 5102 and a warning content to theuser.

FIG. 28 is a schematic sectional view showing an example of the printershown in FIG. 27. FIG. 28 corresponds to, e.g., a tandem color printer.

In FIG. 28, reference numeral 5201 denotes a printer housing; and 5202,an operation panel on which switches for allowing the user to givevarious instructions, an LED display or LCD display for displayingmessages, printer setting contents, and the like are arranged. Theoperation panel 5202 is an example of the panel 5104 shown in FIG. 27.

Reference numeral 5203 denotes a board storage unit which stores a boardconstituting the electronic circuit portions of the video controller5103 and printer engine 5105; and 5220, a sheet cassette which holdssheets (print media) S and has a mechanism of electrically detecting asheet size by a partition (not shown).

Reference numeral 5221 denotes a cassette clutch having a cam whichpicks up one uppermost sheet from the sheets S stacked in the sheetcassette 5220 and conveying the picked sheet S to a feed roller 5222 bya driving force transmitted from a driving means (not shown). This camintermittently rotates every feed, and feeds one sheet S incorrespondence with one rotation. Reference numeral 5223 denotes a sheetsensor which detects the number of sheets S held in the sheet cassette5220.

The feed roller 5222 conveys the leading end of the sheet S to aregistration shutter 5224. The registration shutter 5224 presses thesheet S to stop feed.

Reference numeral 5230 denotes a manual feed tray; and 5231, a manualfeed clutch. The manual feed clutch 5231 is used to convey the leadingend of the sheet S to a manual feed roller 5232, and the manual feedroller 5232 is used to convey the leading end of the sheet S to theregistration shutter 5224. The sheet S used to print an image is fedfrom a selected one of the sheet cassette 5220 and manual feed tray5230.

The printer engine 5105 communicates with the video controller 5103 inaccordance with a predetermined communication protocol. The printerengine 5105 selects either one of the sheet cassette 5220 and manualfeed tray 5230 in accordance with an instruction from the videocontroller 5103, and conveys a sheet S to the registration shutter 5224by a corresponding feed means in accordance with a printing startinstruction. Note that the printer engine 5105 includes a feed means, amechanism concerning an electrophotographic process such as latent imageformation, transfer, and fixing, a discharge means, and control meanstherefor.

Reference numerals 5204 a, 5204 b, 5204 c, and 5204 d denote imageprinting units having photosensitive drums 5205 a, 5205 b, 5205 c, and5205 d, toner holding portions, and the like. The image printing units5204 a to 5204 d form toner images on the sheet S by theelectrophotographic process.

Reference numerals 5206 a, 5206 b, 5206 c, and 5206 d denote laserscanners which supply pieces of image information by laser beams to theimage printing units. A sheet convey belt 5250 for conveying the sheet Sis stretched flat by a plurality of rotational rollers 5251 to 5254 inthe sheet convey direction (upward from a lower portion in FIG. 28) withrespect to the image printing units 5204 a, 5204 b, 5204 c, and 5204 d.At the uppermost stream portion, the sheet is electrostatically chuckedto the sheet convey belt 5250 by a biased attraction roller 5225. Thefour photosensitive drums 5205 a, 5205 b, 5205 c, and 5205 d arearranged straight so as to face the belt convey surface, constituting animage forming means. Each of the image printing units 5204 a, 5204 b,5204 c, and 5204 d comprises a charging unit and developing unitsequentially around the photosensitive drum.

In the laser scanners 5206 a, 5206 b, 5206 c, and 5206 d, referencenumerals 5207 a, 5207 b, 5207 c, and 5207 d denote lasers which driveinternal semiconductor lasers and emit laser beams in accordance withimage signals (/VIDEO signals) sent from the video controller 5103.Laser beams emitted by the lasers 5207 a, 5207 b, 5207 c, and 5207 d arescanned by polygon mirrors (rotary polygon mirrors) 5208 a, 5208 b, 5208c, and 5208 d, and form latent images on the photosensitive drums 5205a, 5205 b, 5205 c, and 5205 d.

Reference numeral 5260 denotes a fixing unit which thermally fixes, tothe print sheet S, toner images formed on the sheet S by the imageprinting units 5204 a, 5204 b, 5204 c, and 5204 d; 5261, a convey rollerwhich discharges and conveys the sheet S; 5262, a discharge sensor whichdetects the discharge state of the sheet S; 5263, a discharge roller &double-sided printing convey path switching roller which conveys thesheet S in the discharge direction, if the convey instruction for thesheet S is “discharge”, directly discharges the sheet S to a dischargetray 5264, if the convey instruction is “double-sided convey”, reversesthe rotational direction immediately after the trailing end of the sheetS passes through the discharge sensor 5262, and conveys the sheet S to adouble-sided printing convey path 5270 by switchback; and 5265, adischarged-sheet stack amount sensor which detects the number of sheetsS stacked on the discharge tray 5264.

On the double-sided printing convey path 5270, the sheet S which isconveyed for double-sided printing by the discharge roller &double-sided printing convey path switching roller 5263 is conveyedagain to the registration shutter 5224 by double-sided convey rollers5271 to 5274, and waits for a convey instruction to the image printingunits 5204 a, 5204 b, 5204 c, and 5204 d.

Note that the printer engine of the 11th embodiment is a mechanism whichsuffers restrictions such that a sheet cannot temporarily stand by onthe double-sided printing convey path or sheets cannot be alternatelyand continuously fed from the double-sided printing convey path and feedtray due to the mechanical structure. More specifically, the printerengine of the 11th embodiment cannot temporarily stop conveyance of aprint sheet having undergone single-sided printing on the double-sidedprinting convey path during image print processing while a fed printsheet is conveyed. To continuously perform double-sided print processingby a highest-speed printing sequence (e.g., double-sided printprocessing is scheduled to a 4-page double-sided sequence, like example{circle around (1)} in FIG. 32), sheets conveyed within the apparatusmust be discharged at a predetermined page interval.

Note that the printer 5102 can be further equipped with optional unitssuch as an optional cassette and envelope feeder.

FIG. 29 is a block diagram showing an arrangement of the printer engine5105 and a video interface which connects the video controller 5103 andprinter engine 5105 shown in FIG. 27.

In FIG. 29, the video controller 5103 executes communication (includingreception of image information) with a plurality of data processingdevices 5101, generation (mapping) of raster data based on receivedimage information, and control of the printer engine 5105.

An engine controller 5150 controls units 5151 to 5158 within the printerengine 5105 on the basis of control signals supplied from the videocontroller 5103.

The outline of the units 5151 to 5158 will be described. The sheet sizedetector 5151 detects the size of a sheet stacked in the sheet cassette5220 or another optional cassette (not shown) and notifies the enginecontroller 5150 of the sheet size.

The feed port detector 5152 detects the presence/absence of the feedport of each of the sheet cassette 5220, manual feed tray 5230, optionalcassette (not shown), and envelope feeder (not shown), and notifies theengine controller 5150 of the detection result.

The option check unit 5153 confirms the connection status of an optionsuch as an optional cassette or envelope feeder. The convey controller5154 controls sheet convey. The optical system controller 5155 controlsthe driving motors of the polygon mirrors 5208 a, 5208 b, 5208 c, and5208 d, and optical systems such as the lasers 5207 a, 5207 b, 5207 c,and 5207 d.

The fixing unit temperature controller 5156 controls the temperature ofa fixing unit 5260, and detects an error in the fixing unit 5260 or thelike. The option controller 5157 controls an option such as an optionalcassette or envelope feeder.

The sensor 5158 detects the presence/absence of a sheet on the conveypath such as registration, discharge, double-sided printing, or reverse,and an environmental change (situation change) such as the outertemperature, the number of print pages, or the residual toner amount.

The outline of signals for a video interface which connects the videocontroller 5103 and engine controller 5150 will be explained.

Reference numeral 5170 denotes a /CPRDY signal representing that thevideo controller 5103 can communicate with the engine controller 5150;and 5171, a /PPRDY signal representing that the engine controller 5150can communicate with the video controller 5103.

Reference numeral 5172 denotes a /RDY signal representing that theengine controller 5150 is in a printable state; 5173, a /PRNT signalwith which the video controller 5103 issues a printing request to theengine controller 5150; and 5174, a /TOP signal functioning as avertical sync signal which is output from the engine controller 5150 tothe video controller 5103.

Reference numeral 5176 denotes a /BD signal functioning as a horizontalsync signal which is output from the engine controller 5150 to the videocontroller 5103; and 5178, a /SCLK signal which is a sync clock signalfor serial communication.

Reference numeral 5179 denotes a /CMD signal which is a command signalfor transmitting a command from the video controller 5103 to the enginecontroller 5150; 5180, a /CBSY signal which is a strobe signal fortransmitting a command; and 5181, a /STS signal functioning as a signalwhich sends back a response (containing the internal status of theprinter engine 5105) with respect to a command transmitted from thevideo controller 5103.

Reference numeral 5182 denotes a /SBSY signal which is a strobe signalfor sending back a response such as status; and 5183, a /VIDEO signalwhich is raster data to be printed.

Reference numeral 5177 denotes a /CCRT (Condition Change Report) signalwhich becomes “TRUE” when a status not directly concerning the /RDYsignal out of the statuses of the printer engine 5105, i.e., a statuschange not directly concerning whether to perform printing occurs (e.g.,the temperature, the number of print pages, or the residual toner amountexceeds a reference value). The above-described signals may be simplyreferred to as signals.

FIG. 30 is a block diagram showing an arrangement of the videocontroller 5103 shown in FIG. 27.

In FIG. 30, reference numeral 5301 denotes a panel interface whichperforms data communication with the panel 5104; and 5309, a CPU whichcontrols a device connected to a CPU bus 5311 on the basis of a controlprogram code held in a ROM 5304, and can confirm contents set anddesignated by the user on the panel 5104 via the panel interface 5301.

Reference numeral 5302 denotes a host interface which bidirectionallycommunicates with the data processing device 5101 such as a hostcomputer via a network; and 5306, an engine interface which communicateswith the printer engine 5105. The CPU 5309 can control the signals 5170,5173, 5175, 5178, 5179, and 5180 via the engine interface 5306, andrecognize the states of the signals 5171, 5172, 5174, 5176, 5177, 5181,and 5182, i.e., the state of the printer engine 5105.

Reference numeral 5303 denotes an image data generator which generates(rasterizes) raster data supplied to the printer engine 5105 on thebasis of image information supplied from the data processing device5101; and 5305, an image memory which temporarily holds generated rasterdata.

Reference numeral 5307 denotes a RAM which functions as a temporarymemory used by a CPU 5309; 5310, an EEPROM which holds controlinformation such as a density correction table; 5308, a DMA controllerwhich transfers raster data in the image memory 5305 to an engineinterface 5306 in accordance with an instruction from the CPU 5309; and5311, a CPU bus which includes address, data, and control buses.

The panel interface 5301, host interface 5302, image data generator5303, ROM 5304, image memory 5305, engine interface 5306, RAM 5307, DMAcontroller 5308, CPU 5309, and EEPROM 5310 can access all devicesconnected to the CPU bus 5311.

FIG. 31 is a flow chart showing an example of data processing proceduresaccording to the 11th embodiment. These procedures correspond to outputcolor mode attribute change processing procedures in the videocontroller 5103 by the printer engine 5105 which cannot switch the colormode because a sheet exists on the double-sided printing convey path indouble-sided printing. Reference symbols S5101 to S5104 denote steps.Each procedure is executed by the CPU 5309 on the basis of a controlprogram held in the ROM 5304 shown in FIG. 30. The procedures areexecuted for each page after data analysis processing for data receivedby the data processing device 5101 via the host interface 5302.

After output color mode attribute change processing starts, the CPU 5309checks in step S5101 whether the current page is a page subjected todouble-sided designation. If NO in step S5101, the processing endswithout changing the output color mode attribute.

If YES in step S5101, whether the page is a monochrome-designated pageis checked in step S5102. If NO in step S5102, the processing endswithout changing the output color mode attribute.

If YES in step S5102, whether the double-sided sequence subset to whichthe page belongs contains a color-designated page is checked in stepS5103.

The double-sided sequence subset means a page subset such as a 4-pagetype or 2-page type subset obtained when a double-sided sequence isdivided at a position where no sheet exists on the double-sided printingconvey path.

If NO in step S5103, the processing ends without changing the outputcolor mode attribute.

If YES in step S5103, the color mode attribute of the page is forciblychanged to the color print mode in step S5104, and output color modeattribute change processing ends.

FIG. 32 is a view showing an example of a double-sided printing sequencepattern in the printer according to the present invention. FIG. 32corresponds to an example of a sequence pattern which can be scheduledin double-sided printing for the printer engine 5105 that cannot switchthe color mode because a sheet exists on the double-sided printingconvey path in double-sided printing.

The sequence pattern example as shown in FIG. 32 is a special sequencepattern formed under restrictions such that a sheet cannot temporarilystand by on the double-sided printing convey path or sheets cannot bealternately and continuously fed from the double-sided printing conveypath and feed tray due to the mechanical structure.

The difference between conditions for forming a sequence with a 4-pagetype pattern in example {circle around (1)} and a 2-page type pattern inexample {circle around (2)} is the difference in schedulable sheet sizerestriction or the difference in time taken for rendering processing ofa page to be scheduled (drawing object rasterizing processing).

At this time, if the sheet size is large or the rendering time of a pageto be scheduled is long, pages are scheduled such that sheets circulateby the number of sheets smaller than a circulable number of sheets onthe double-sided printing convey path, like example {circle around (2)},suppressing a decrease in printing throughput.

As shown in FIG. 32, in double-sided printing for four pages: page P1 topage P4 (P1 to P4), the pages are scheduled into, e.g., the followingsequence pattern in consideration of the attribute and rendering time ofpages to be scheduled.

In example {circle around (1)}, pages are scheduled into a 4-page typedouble-sided sequence. The order in the 4-page sequence is P2→P4→P1→P3.

In example {circle around (2)}, pages are scheduled into a 2-page typedouble-sided sequence. The order in the 2-page sequence is P2→P1→P4→P3.

After the double-sided sequence is scheduled in the above way,processing shown in FIG. 31 is applied to decide a color mode in outputof each double-sided sequence subset.

FIG. 33 is a view for explaining a print mode switching sequence statein the printer according to the present invention. FIG. 33 correspondsto an example of the result of performing output color mode attributechange processing for a scheduled double-sided sequence.

In the example of FIG. 33, 8-page double-sided print data is scheduledinto a double-sided sequence by double-sided scheduling processing suchthat the first two pages (P2 and P1) are scheduled into the 2-page type;four succeeding pages (P4, P6, P3, and P5), into the 4-page type; andthe last two pages (P8 and P7), into the 2-page type.

Output color mode attribute change processing shown in the flow chart ofFIG. 31 is executed for this double-sided sequence. The first two pages(P2 and P1) are monochrome pages, and their color mode attributes keepthe monochrome print mode without any change. Four succeeding pages (P4,P6, P3, and P5) contain color-designated page P6, and the color modeattributes of pages P4, P3, and P5 as monochrome pages are changed tothe color print mode. The last two pages (P8 and P7) containcolor-designated page P7, and the color mode attribute of page P8 as amonochrome page is changed to the color print mode.

In this fashion, output color mode attribute change processing isperformed for each double-sided sequence subset after double-sidedsequence scheduling. In scheduling a double-sided sequence, the sequenceneed not be divided into, e.g., 2-page type sequences with a lowthroughput by faithfully complying with a color mode designated fororiginal data.

In scheduling a double-sided sequence, a double-sided sequence whichignores a color mode designated for original data and is made up of onlyother conditions is formed. Output color mode attribute changeprocessing is done for the formed double-sided sequence. Even a specialsequence under restrictions on the printer engine can prevent color modeswitching within the subset.

FIGS. 34, 35, 36, and 37 are timing charts for explaining a print dataprocessing state according to the 11th embodiment. FIGS. 34, 35, 36, and37 correspond to some of processing examples in the printer when 4-pagedouble-sided print data is received. Reference symbols S5201 to S5234and S5301 to S5335 denote steps.

The example shown in FIGS. 34 and 35 concerns scheduling into a 4-pagetype double-sided sequence. The example shown in FIGS. 36 and 37concerns scheduling into a 2-page type double-sided sequence.

In FIGS. 34 and 35, the printer 5102 receives 4-page double-sided printdata from the host computer 5101. The CPU 5309 of the video controller5103 then performs processing of interpreting PDL data and converting itinto intermediate data (display list) and page attribute information.The printing controller of the engine I/F 5306 is notified by the hostI/F 5302 that print data has been received (S5201). The printingcontroller of the engine I/F 5306 which has received the notificationinstructs the image data generator 5303 to start rendering processingfor page P1 (S5202).

After the image data generator 5303 sends back a rendering processingcompletion notification for page P1 to the printing controller (S5203),the printing controller instructs the image data generator 5303 to startrendering processing for page P2 (S5204), and waits for a completionnotification.

The image data generator 5303 sends back a rendering processingcompletion notification for page P2 to the printing controller (S5205),ending rendering processing of the two pages. For double-sided printing,the printing controller estimates the rendering processing times ofsubsequent pages P3 and P4, and checks whether pages P1 to P4 can bescheduled as a 4-page type double-sided sequence. In the example ofFIGS. 34 and 35, it is determined that pages P1 to P4 can be scheduledinto a 4-page type double-sided sequence. The printing order is pageP2→page P4→page P1→page P3 (scheduling). After that, renderingprocessing is similarly executed for pages P3 and P4.

In step S5206, the printing controller instructs the image datagenerator 5303 to start rendering processing for page P3. After theimage data generator 5303 sends back a rendering processing completionnotification for page P3 to the printing controller (S5207), theprinting controller instructs the image data generator 5303 to startrendering processing for page P4 (S5208).

After the image data generator 5303 sends back a rendering processingcompletion notification for page P4 to the printing controller (S5209),the printing controller performs output color mode attribute changeprocessing for pages P1 to P4 decided as a double-sided sequence subset.If the subset contains a color-designated page, the color mode attributeof a monochrome page in the subset is changed to “color print mode”.

In the example of FIGS. 34 and 35, page P3 is a color-designated page.The color mode attributes of the remaining monochrome pages P1, P2, andP4 are changed to “color print mode”.

After the output color mode is decided for the subset of pages P1 to P4,the setting of the printer engine 5105 must be changed.

If the color mode of the printer engine 5105 is the same as the outputcolor mode of the page subset to be printed, the current setting stateneed not be changed.

In step S5210, the printing controller issues a color print modeinstruction for outputting the subset of pages P1 to P4 in “color printmode” when the mode setting of the printer engine 5105 is “monochromeprint mode”.

After the color print mode instruction, the printing controller issues afeed start instruction to the printer engine 5105 in accordance with theprinting order. In step S5211, the printing controller issues a feedstart instruction for page P2.

Note that the timings of steps S5210 and S5211 may be earlier inaccordance with the estimation of the rendering processing times ofpages P3 and P4 after sequence decision.

The double-sided sequence decision timing may be a timing after pagegeneration in step S5201 by estimating the rendering time. Renderingprocessing may be sequentially performed in accordance with the pageorder.

After the feed start instruction for page P2, the printer engine 5105outputs the/TOP signal 5174 serving as a vertical sync signal (S5212).The printing controller then issues, to the image data generator 5303and DMA controller 5308, a banding processing start instruction fortransmitting image data for each band to the printer engine 5105 (S5213and S5214).

Upon reception of the banding processing start instruction, the DMAcontroller 5308 transfers image data to the printer engine 5105 whileperforming predetermined banding processing (S5215).

At the reception timing of the /TOP signal 5174 from the printer engine5105, the printing controller issues a feed start instruction for pageP4 as a page to be printed next (S5216).

The printing controller receives a banding completion notification forpage P2 from the image data generator 5303 (S5217). After that, theprinter engine 5105 outputs the /TOP signal 5174 for page P4, similar topage P2 (S5218). This processing is sequentially executed up to stepS5234.

In FIGS. 36 and 37, the printer 5102 receives 4-page double-sided printdata from the host computer 5101. The CPU 5309 of the video controller5103 then performs processing of interpreting PDL data and converting itinto intermediate data (display list) and page attribute information.The printing controller in the engine I/F 5306 is notified by the hostI/F 5302 that print data has been received (S5301). The printingcontroller in the engine I/F 5306 which has received the notificationinstructs the image data generator 5303 to start rendering processingfor page P1 (S5302). After the image data generator 5303 sends back arendering processing completion notification for page P1 to the printingcontroller (S5303), the printing controller instructs the image datagenerator 5303 to start rendering processing for page P2 (S5304), andwaits for a completion notification.

The image data generator 5303 sends back a rendering processingcompletion notification for page P2 to the printing controller (S5305),ending rendering processing of the two pages. For double-sided printing,the printing controller estimates the rendering processing times ofsubsequent pages P3 and P4, and checks whether pages P1 to P4 can bescheduled as a 4-page type double-sided sequence.

In the example of FIGS. 36 and 37, it is determined that pages P1 to P4cannot be scheduled into a 4-page type double-sided sequence, and pagesP1 to P4 are scheduled into 2-page type double-sided sequences. Thesubset of former two pages has a printing order of page P2→page P1, andthe subset of latter two pages has a printing order of page P4→page P3(scheduling)

In step S5306, the printing controller instructs the image datagenerator 5303 to start rendering processing for page P3. At the sametime, in order to perform print processing for the subset of the formertwo pages (pages P2 and P1), the printing controller executes outputcolor mode attribute change processing for pages P2 and P1. If thesubset contains a color-designated page, the color mode attribute of amonochrome page in the subset is changed to the color print mode.

In the example of FIGS. 36 and 37, both pages P1 and P2 are monochrome,and their output color mode attributes keep the monochrome print modewithout any change. After the output color mode is decided for thesubset of pages P1 and P2, the setting of the printer engine 5105 mustbe changed.

If the color mode of the printer engine 5105 is the same as the outputcolor mode of the page subset to be printed, the setting need not bechanged.

In step S5307, the printing controller issues a monochrome print modeinstruction in order to output the subset of pages P1 and P2 in themonochrome print mode when the mode setting of the printer engine 5105is the color print mode.

After the “monochrome print mode” instruction, the printing controllerissues a feed start instruction to the printer engine 5105 in accordancewith the printing order. In step S5308, the printing controller issues afeed start instruction for page P2. After the feed start instruction forpage P2, the printer engine 5105 outputs the /TOP signal 5174 (S5309).The printing controller then issues, to the image data generator 5303and DMA controller 5308, a banding processing start instruction fortransmitting image data for each band to the printer engine 5105 (S5310and S5311).

Upon reception of the banding processing start instruction, the DMAcontroller 5308 transfers image data to the printer engine 5105 whileperforming predetermined banding processing (S5312). After image datatransfer processing ends, the printing controller receives a bandingprocessing completion notification for page P2 from the image datagenerator 5303 (S5313).

After the image data generator 5303 sends back a rendering processingcompletion notification for page P3 to the printing controller (S5314),the printing controller instructs the image data generator 5303 to startrendering processing for page P4 (S5315), and waits for a completionnotification.

The printing controller issues a feed start instruction for page P1serving as a page to be printed next (step S5316). The printer engine5105 outputs the /TOP signal 5174 for page P1 (S5317), and the printingcontroller which has received the /TOP signal 5174 issues a bandingprocessing start instruction to the image data generator 5303 and DMAcontroller 5308 (S5318 and S5319).

Upon reception of the banding processing start instruction, the DMAcontroller 5308 transfers image data to the printer engine 5105 whileperforming predetermined banding processing (S5320). After image datatransfer processing ends, the printing controller receives a bandingprocessing completion notification for page P1 from the image datagenerator 5303 (S5321).

After the image data generator 5303 sends back a rendering processingcompletion notification for page P4 to the printing controller (S5322),the printing controller performs double-sided scheduling for theremaining pages P3 and P4.

If no succeeding page exists, pages P3 and P4 are scheduled into a2-page type double-sided sequence. The printing controller executesoutput color mode attribute change processing for pages P3 and P4. Ifthe subset contains a color-designated page, the color mode attribute ofa monochrome page in the subset is changed to “color print mode”.

In the example of FIGS. 36 and 37, page P3 is color. The color modeattribute of monochrome page P4 is changed to “color print mode”. After“color print mode” is decided as the output color mode for pages P3 andP4, the setting of the printer engine 5105 must be changed.

In this case, the color mode of the printer engine 5105 is set to“monochrome print mode” in order to print pages P1 and P2. Thus, theprinting controller instructs the printer engine 5105 of “color printmode” in step S5323.

As for page P4, the printing controller issues a feed start instructionto the printer engine 5105 (step S5324). After the feed startinstruction for page P4, the printer engine 5105 outputs the /TOP signal5174 (S5325). The printing controller then issues, to the image datagenerator 5303 and DMA controller 5308, a banding processing startinstruction for transmitting image data for each band to the printerengine 5105 (S5326 and S5327).

Upon reception of the banding processing start instruction, the DMAcontroller 5308 transfers image data to the printer engine 5105 whileperforming predetermined banding processing (S5328).

The printing controller receives a banding completion notification forpage P4 from the image data generator 5303 (S5329). Processes fromissuing of a feed start instruction (S5330) to step S5335 aresequentially performed for page P4.

12th Embodiment

In the 11th embodiment, if the page subset contains even onecolor-designated page, the color mode attributes of the remainingmonochrome pages are changed to “color print mode” in order to make thecolor mode attributes of pages within a double-sided sequence subsetcoincide with each other in a printer engine which cannot switch theprint mode while a sheet exists on the double-sided printing convey pathin double-sided printing. Also in a printer engine having a mechanism(to be referred to as a 2-page formation mode hereinafter) of conveyingprint media two by two in printing and forming images on two pages at atime, the color mode attribute of a monochrome page may be changed to“color print mode” in the presence of a color-designated page in a pagesubset in order to make color mode attributes coincide with each otherwithin a 2-page subset scheduled as the 2-page formation mode. In the12th embodiment, the control for an image forming apparatus will bedescribed.

FIG. 38 is a flow chart showing an example of data processing proceduresaccording to the 12th embodiment. These procedures correspond to outputcolor mode attribute change processing procedures in a video controller5103 by, e.g., a printer engine having the 2-page formation mechanism.These procedures are executed by a CPU 5309 on the basis of a controlprogram held in a ROM 5304, and done for each page after data analysisprocessing for data received from a data processing device 5101 via ahost interface 5302.

After output color mode attribute change processing starts, the CPU 5309checks in step S5501 whether the current page is a page determined thatit can be output in the 2-page formation mode. If NO in step S5501, theprocessing ends without changing the output color mode attribute.

If YES in step S5501, whether the page is a monochrome-designated pageis checked in step S5502. If NO in step S5502, the processing endswithout changing the output color mode attribute.

If YES in step S5502, whether the 2-page formation sequence subset towhich the page belongs contains a color-designated page is checked instep S5503. The 2-page formation sequence subset is a page subset suchas a 1-page formation mode or 2-page formation mode divided every imageformation. If NO in step S5503, the processing ends without changing theoutput color mode attribute.

If YES in step S5503, the color mode attribute of the page is forciblychanged to “color print mode” in step S5504, and output color modeattribute change processing ends.

FIG. 39 is a view for explaining a print mode switching sequence stateaccording to the 12th embodiment. FIG. 39 corresponds to an example ofthe result of performing output color mode attribute change processingshown in FIG. 38 for a scheduled image formation mode.

In example {circle around (1)} of FIG. 39, the first two pages P1 and P2out of single-sided print data of four pages are scheduled into the2-page formation mode by single-sided scheduling processing, and twosubsequent pages P3 and P4 are also scheduled into the 2-page formationmode. In output color mode attribute change processing performed forthis sequence, the first two pages P1 and P2 are monochrome pages, andtheir color mode attributes keep the monochrome print mode without anychange. The two subsequent pages P3 and P4 contain color-designated pageP3, and the color mode attribute of monochrome page P4 is changed to thecolor print mode.

In example {circle around (2)}, each page out of single-sided print dataof four pages is scheduled into the 1-page formation mode bysingle-sided scheduling processing. The color mode attribute need not bechanged for the sequence in the 1-page formation mode, and data isprinted in accordance with a color mode attribute designated for thedata.

In example {circle around (3)}, the first page P2 and next page P4 outof double-sided print data of eight pages are scheduled into the 1-pageformation mode by double-sided scheduling processing. Two subsequentpages P1 and P6 and two subsequent pages P3 and P8 are scheduled intothe 2-page formation mode, and page P5 and the final page P7 arescheduled into the 1-page formation mode.

By performing output color mode attribute change processing for thedouble-sided sequence which can be output with the highest throughput,the color mode attribute of monochrome page P8 in the subset containingcolor-designated page P3 out of sequence subsets in the 2-page formationmode is changed to the color print mode.

In this manner, also in a printer engine having the mechanism ofconveying print media two by two in printing and forming images on twopages at a time, the color mode attribute of a monochrome page ischanged to the color print mode in the presence of a color-designatedpage in a page subset in order to make color mode attributes coincidewith each other within a 2-page subset scheduled as the 2-page formationmode. This increases the frequency of scheduling pages in the 2-pageformation mode which maximizes the throughput. Consequently, a decreasein throughput by switching the monochrome/color print mode can beprevented.

13th Embodiment

In the 11th embodiment, color mode attribute change processing targetsonly a page assigned double-sided printing. Color mode attribute changeprocessing may target a page assigned single-sided printing.

When a monochrome page sandwiched between color pages, a page in amonochrome page subset sandwiched between color pages, or a monochromepage which is subsequent to a color page and has no next page exists inprint data containing only pages assigned single-sided printing or printdata containing pages assigned double-sided printing and pages assignedsingle-sided printing, the color mode attribute of the monochrome pageis changed to the color print mode. This can reduce switching betweenthe monochrome and color print modes.

14th Embodiment

In the 12th embodiment, color mode attribute change processing targetsonly a page subset scheduled in the 2-page formation mode. Color modeattribute change processing may target a page scheduled in the 1-pageformation mode.

When a page scheduled in the 1-page formation mode is a monochrome pagesandwiched between color pages, a page in a monochrome page subsetsandwiched between color pages, or a monochrome page which is subsequentto a color page and has no next page, the color mode attribute of themonochrome page is changed to the color print mode. This can reduceswitching between the monochrome and color print modes.

15th Embodiment

In the 13th and 14th embodiments, the color mode attribute of a page isso forcibly changed as not to change the print process mode as much aspossible. However, the color mode attribute of a page may be socontrolled as not to be forcibly changed more than necessary if it canbe estimated that the entire throughput is not influenced withoutswitching from the monochrome print mode to the color print mode or fromthe color print mode to the monochrome print mode in consideration ofthe data processing time of rendering processing or the like, thestandby time required to switch the feed stage in printing, and thelike.

As described above, according to the above embodiments, if the pagesubset contains a color-designated page, the color mode attribute of amonochrome page in the subset is changed to the color print mode inorder to make color mode attributes coincide with each other within thepage subset divided at a position where no sheet exists on thedouble-sided printing convey path in a printer engine which cannotswitch the print mode while a sheet exists on the double-sided printingconvey path in double-sided printing. The double-sided sequence whichhas a maximum throughput can be implemented.

Also in a printer engine having the mechanism of conveying print mediatwo by two in printing and forming images on two pages at a time, thecolor mode attribute of a monochrome page is changed to the color printmode in the presence of a color-designated page in a page subset inorder to make color mode attributes coincide with each other within a2-page subset scheduled as the 2-page formation mode. This increases thefrequency of scheduling pages in the 2-page formation mode whichmaximizes the throughput.

As a result, even in a printer engine which undesirably decreases thethroughput depending on the page layout of print data due to switchingof the monochrome/color print mode, the schedule of a print sequence forprint data containing monochrome and color pages can be optimized. Adecrease in throughput can be suppressed, increasing the print dataprocessing efficiency.

As has been described above, it is possible to limit print modeswitching, suppress a decrease in throughput, and increase the printdata processing efficiency when a printer with a printing mechanismwhich requires processing of temporarily stopping a print sequence inswitching between the color and monochrome print modes processes printdata containing pages assigned monochrome printing and pages assignedcolor printing, or print data containing pages assigned monochromeprinting and pages assigned color printing in double-sided printing.

The object of the present invention is also achieved when a storagemedium which stores software program codes for realizing the functionsof the above-described embodiments is supplied to a system or apparatus,and the computer (or the CPU or MPU) of the system or apparatus readsout and executes the program codes stored in the storage medium.

In this case, the program codes read out from the storage medium realizethe new functions of the present invention, and the storage medium whichstores the program codes constitutes the present invention.

The storage medium for supplying the program codes includes a flexibledisk, hard disk, optical disk, magnetooptical disk, CD-ROM, CD-R,magnetic tape, nonvolatile memory card, ROM, and EEPROM.

The functions of the above-described embodiments are realized when thecomputer executes the readout program codes. Also, the functions of theabove-described embodiments are realized when an OS (Operating System)running on the computer performs part or all of actual processing on thebasis of the instructions of the program codes.

The functions of the above-described embodiments are also realized whenthe program codes read out from the storage medium are written in thememory of a function expansion board inserted into the computer or thememory of a function expansion unit connected to the computer, and theCPU of the function expansion board or function expansion unit performspart or all of actual processing on the basis of the instructions of theprogram codes.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

1. A printer having a full-color print process and a monochrome printprocess, comprising: color/monochrome discrimination means fordiscriminating whether an attribute of a target page to be printed iscolor or monochrome; first determination means for determining presenceof an immediately preceding page which is successively printed beforethe target page determined to be monochrome by said color/monochromediscrimination means; second determination means for determiningpresence of a succeeding page which is successively printed after thetarget page determined to be monochrome by said color/monochromediscrimination means, and an attribute of the succeeding page; and printprocess decision means for setting number of pages in accordance withwhether or not said first determination means has determined that theimmediately preceding page is present, and deciding a print process forthe target page on the basis of presence and attributes of subsequentpages corresponding to the number of pages that are determined by saidsecond determination means.
 2. The printer according to claim 1, whereinthe attribute includes a print process, a size of a print medium usedfor printing, a type of print medium, or a combination of the printprocess, the size of the print medium, and the type of print medium. 3.The printer according to claim 1, wherein when said first determinationmeans determines that the immediately preceding page exists and theprint process of the immediately preceding page is monochrome printing,said print process decision means decides the monochrome print processas the print process of the page to be printed.
 4. The printer accordingto claim 1, wherein when said second determination means determines thatsubsequent pages corresponding to the number of pages contain afull-color page, said print process decision means decides thefull-color print process as the print process of the page to be printed.5. The printer according to claim 1, wherein when said seconddetermination means determines that subsequent pages corresponding tothe number of pages do not exist but subsequent pages contain afull-color page, said print process decision means decides thefull-color print process as the print process of the page to be printed.6. The printer according to claim 2, wherein when second determinationmeans determines that a subsequent page contains a change in the size ofthe print medium and/or a change in the type of print medium, said printprocess decision means decides the monochrome print process as the printprocess of the page to be printed.
 7. The printer according to claim 2,wherein when said second determination means determines that subsequentpages corresponding to the number of pages contain a full-color page andthe attribute does not change, said print process decision means decidesthe full color print process as the print process of the page to beprinted.
 8. The printer according to claim 1, wherein said print processdecision means decides a print process in accordance with a userinstruction.
 9. The printer according to claim 1, wherein said printprocess decision means decides a print process in accordance withdesignation from a printer driver of a host device.
 10. A method ofcontrolling a printer having a full-color print process and a monochromeprint process, comprising: the color/monochrome discrimination step ofdiscriminating whether an attribute of a target page to be printed iscolor or monochrome; the first determination step of determiningpresence of an immediately preceding page which is successively printedbefore the target page determined to be monochrome in thecolor/monochrome discrimination step, the second determination step ofdetermining presence of a succeeding page which is successively printedafter the target page determined to be monochrome in thecolor/monochrome discrimination step, and an attribute of the succeedingpage; and the print process decision step of setting number of pages inaccordance with whether or not said first determination means hasdetermined that the immediately preceding page is present, and decidinga print process for the page on the basis of presence and attributes ofsubsequent pages corresponding to the number of pages that aredetermined in the second determination step.
 11. The method according toclaim 10, wherein the attribute includes a print process, a size of aprint medium used for printing, a type of print medium, or a combinationof the print process, the size of the print medium, and the type ofprint medium.
 12. The method according to claim 10, wherein when thepresence of the immediately preceding page is determined in the firstdetermination step and the print process of the immediately precedingpage is determined to be monochrome printing, the monochrome printprocess is decided as the print process of the page to be printed in theprint process decision step.
 13. The method according to claim 10,wherein when subsequent pages corresponding to the number of pages aredetermined in the second determination step to contain a full-colorpage, the full-color print process is decided as the print process ofthe page to be printed in the print process decision step.
 14. Themethod according to claim 10, wherein when subsequent pagescorresponding to the number of pages are determined in the seconddetermination step not to exist but subsequent pages are determined tocontain a full-color page, the full-color print process is decided asthe print process of the page to be printed in the print processdecision step.
 15. The method according to claim 11, wherein when asubsequent page is determined in the second determination step tocontain a change in the size of the print medium and/or a change in thetype of print medium, the monochrome print process is decided as theprint process of the page to be printed in the print process decisionstep.
 16. The method according to claim 11, wherein when subsequentpages corresponding to the number of pages are determined in the seconddetermination step to contain a full-color page and the attribute isdetermined not to change, the full-color print process is decided as theprint process of the page to be printed in the print process decisionstep.
 17. The method according to claim 10, wherein a print process isdecided in the print process decision step in accordance with a userinstruction.
 18. The method according to claim 10, wherein a printprocess is decided in the print process decision step in accordance withdesignation from a printer driver of a host device.